Ask HN: What trick of the trade took you too long to learn?
100 comments
·August 4, 2025oumua_don17
Start as early as possible in investing (in index funds) and otherwise being financially savvy. It is very beneficial to realise early on that growing your hard earned money and spending it wisely is way more important as it will in the future lead to some unexpected benefits. Freedom of thought and action!
al_borland
My mistake was not starting early, because the numbers were small and it didn’t seem worth the time. The habit and systems are important to build, so that when the numbers do get bigger it goes to the right place.
FristPost
I didn't start investing until I understood it.
This is a fantastic course. It covers a lot of ground.
If you want to actively invest, this will help you learn the mechanics. But in the end, what you really learn, is that you can't beat the market.
https://ocw.mit.edu/courses/15-401-finance-theory-i-fall-200...
Terretta
Call Vanguard: 877-662-7447
An investing prof at Chicago puts this on the whiteboard at the start of semester, saying this is really all most people need to know and this class is unlikely to learn anything in his or any class that will let them, personally, do better.
lurking_swe
That’s good advice for a layman but most high earners can do much better if they care and are motivated. Most are neither though lol.
Mostly on the tax side. Some specific examples:
- after maxing out your 401k what should you do next? IRA? Mega backdoor roth? Something else?
- If you have kids, how to best save for future education expenses? Hint: consider 529 plan.
- HSA is technically the best tax advantaged account, most high earners don’t realize it and “waste” the HSA funds to reimburse typical medical bills. HSA has triple tax benefits: contributions are tax-free, growth is tax-free, and withdrawals are also tax-free after age 65 for any reason, not just medical expenses. So basically investing without any tax obligation. You can also withdraw tax free before 65, but for medical expenses only.
i could go on…investing is great, but reducing your tax obligation is an even more powerful technique if you want to grow your net worth.
xhrpost
Looked into HSA recently at work but legally you need a high deductible health care plan to be eligible. Looking at the options, just nothing looked good compared to my current $0 deductible/$0 co-pay plan. Hard to know for sure but just seemed like I would be paying a lot more out of pocket every year.
matt_s
What you have stated is almost the same as call Vanguard, all those options are the same in the sense that they all involve investing, leaving it alone for a long time. Its just the vehicle thats slightly different and tax advantages.
I wouldn’t consider those options needing much motivation or research. The key with all of them is investing early and leaving it alone.
arjvik
The HSA thing intrigued me and so I did some digging. It appears that post-65, you still have to pay income tax on non-medical withdrawals from an HSA? That is, besides the tax-free-for-medical-expenses part it reverts to a traditional IRA?
One additional trick though is that it looks like you can pay for any HSA-eligible medical expenses (incurred after you created the HSA) out-of-pocket now, and reimburse your bills at any point in the future? Thus you can still earn interest on the cash before withdrawing it at any point in the future (treating it as tax-free liquidity).
(I don't fully understand this so these are questions not statements, but hopefully I'm correct!)
d_burfoot
#1 Rule of Investing: you can't beat the market, but you can beat the tax man
davidivadavid
At that point get someone to do it for you for x% of what they're getting you back and live blissfully unaware of arcane tax code specifics.
1oooqooq
i tried that hack one year. Cigna just emptied my account on the first try with a provider charging 2 emergency room visits when I was there only for a xray.
Cigna refused to lift a finger unless i sued them both.
yeah, i wouldn't recommend that.
scarface_74
This is generally not applicable to most people.
1. Invest enough to get the company match in an S&P 500. It probably isn’t Vanguard that your company uses
2. Pay off all of your debt except your house (and maybe your car)
3. Max out your HSA - if you are married it’s - $8550
4. Max out your 401K - again that’s probably not through Vanguard - $23500
5. Step 5 - then call Vanguard and depending on your income just do a Roth up to $8000 (?).
(Unless you are over 50 then do catch up contributions as 4.5)
If you are under 50, you can do $40,500 tax advantaged and over 50 $48050
monkeyelite
Why are we advertising this particular broker?
arjvik
Vanguard is one of the cooler-structured brokerages. Vanguard (the management firm) is owned by the mutual funds themselves, of which you are an investor of. So their shareholder obligation is genuinely towards "clients" of the individual mutual funds. As far as I'm aware, this is the only mutually-owned mutual fund firm.
It's definitely got a solid track record and good fees, but these are things I'd feel weird about advertising it on HN for.
nemomarx
vanguards very large and they're a mutual fund, so they have a lower profit motive than most brokers for it. they're basically the standard retirement fund company now
jkmcf
My millionaire, step-father-in-law, gave this advice to my brother when graduated.
I was lucky, my physics department administrator told me the same thing when I was graduating.
The 2ND best piece of advice is to rollover your 401k when you move to a new company -> this cost me at least 500k because they effectively stagnate when your company isn't paying the maintenance cost (AIUI).
slapstick
> this cost me at least 500k because they effectively stagnate when your company isn't paying the maintenance cost
Is this true? My understanding is that the fees come out of the account itself. There's other good reasons to roll over (primarily investment flexibility) but I have not heard of something like this.
bcyn
I don't think the point about 401k stagnation is true. At most fee structures and optionality of funds change. How did that cost you 500k exactly?
emmelaich
Get a financial advisor that you trust.
david422
When you buy a house and get a mortgage, you are going to be paying MUCH more in interest (than expected). Over the course of the mortgage, you are going to be paying MUCH more than the sticker price. Between closing costs and taxes and fees maintenance, you will need more cash than you think.
My advice is look at the numbers very carefully and choose something that is (below) or fits your budget. Sudden financial issues like the loss of a job or new vehicle purchase can put a big strain on all this.
mitthrowaway2
What do you do when the people you're bidding against don't understand this?
bozhark
Exactly, calculate total cost of loan vs. cost of purchase
tibbar
You can memorize the correct opening moves in chess. For maybe my first year playing chess, I just YOLO'd the opening moves. My judgement there was probably not much worse than the rest of my play, but with other players playing engine moves in the opening, I was probably in a losing position early on in most of my games. I gained about, I think, 100 ELO after learning some 3 or 4 move opening combinations.
yummypaint
Most problems (including analytically intractible ones) can be modeled with a relatively simple monte-carlo simulation. Most simple monte-carlo simulations can be fully implemented in a spreadsheet.
Using timing coincidences in particle physics experiments is incredibly powerful. If multiple products from the same reaction can be measured at once, it's usually worth looking into.
Circular saws using wood cutting blades with carbide teeth can cut aluminum plates.
You can handle and attach atomically thin metal foils to things by floating them on water.
Use library search tools and academic databases. They are entirely superior to web search and AI.
abetusk
I feel like the Monte-Carlo simulation modeling trick is one I picked up intuitively but only recently heard formalized. Do you (or anyone else) have a list of example problems that are solved in this way? Like a compendium of case studies on how to apply this trick to real world problems?
bobbiechen
_How to Measure Anything_ by Douglas Hubbard includes a chapter on Monte Carlo simulations and comes with downloadable Excel examples: https://www.howtomeasureanything.com/3rd-edition/ (scroll down to Ch. 6)
The main example is, you're considering leasing new equipment that might save you money. What's the risk that it will actually cost more, considering various ranges of potential numbers (and distributions)?
I think it's harder to apply to software since there are more unknowns (or the unknowns are fatter-tailed) but I still liked the book just for the philosophical framing at the beginning: you want to the measure things because they help you make decisions; you don't need perfect measurements since reducing the range of uncertainty is often enough to make the decision.
yummypaint
A simple example that highlights the strength of this method: a 137Cs point source is at the origin. A detector consisting of a right cylinder at arbitrary distance and orientation is nearby. What is the solid angle?
There may exist an analytical solution for this, but I wouldn't trust myself to derive it correctly. It would certainly be a huge mess.
If we add that the source is also a right cylinder instead of point source, and we want to add first order attenuation of emitted gammas by the source itself, the spreadsheet becomes only a bit more complex, but there will not be a pen and paper equation solution.
In this example every row of the spreadsheet would represent a hypothetical ray. One could randomly choose a location in the source, a random trajectory, and check if the photon intersects the detector. An alternative approach would be randomly choosing points in both target and detector, then doing additional math.
The results are recovered by making histograms and computing stats on the outputs of all the rows. You probably need a few thousand for most things at least. Remember roughly speaking 10k hits gets you ~1% statistics.
thrawa8387336
Think of hard problems where sampling of outcomes could give you a better understanding
sceadu
not sure if it counts as a list of case studies, but a relevant and recent video nonetheless https://www.youtube.com/watch?v=KZeIEiBrT_w
also in general bayesian statistics
random medium article: https://medium.com/pythoneers/monte-carlo-simulation-ideas-a...
aghilmort
what do you consider top tier library search tools and academic databases these days?
btrettel
I've used various commercial databases over the years. Some popular commercial databases relevant to HN readers include Web of Science, Scopus, and Engineering Village. When I worked at the USPTO, I used the less popular database Dialog, which I preferred. To my knowledge, none of these are available direct to consumers. I've only been able to get access from places with subscriptions. Some university libraries allow visitors where you can use these databases for free on-site.
I would call these databases complementary, not "entirely superior". There are two main advantages. One is that these databases will contain many things that you can't find on Google. The second advantage of these databases is that they are designed for advanced searchers and have more powerful query languages. Google on the other hand is dumbed down and will try to guess what you want, often doing a poor job. You can get very specific on these databases in ways that you can't with Google.
Related: I'm somewhat fascinated by more specialized bibliographic databases because they often contain things that can't be found on Google or the major commercial databases I listed above. I started keeping a list of them. https://github.com/btrettel/specialized-bibs
1oooqooq
even wood tipped circular saw can cut Al plate...
and academic/library search is indeed so underrated!
thebeardisred
A shell script has to start with "#!" with no spaces before it. I spent about a week figuring that out 25+ years ago.
treetalker
The big one, for keeping my focus on the power of repeated, consistent action, and prioritizing my "future selves":
What is likely to happen if I do (or don't do) this thing one thousand days (or times) in a row?
Examples:
- exercising 2h per day and eating right --> I'm going to look and feel great and my health will be far better than that of my peers
- Should I buy these cookies along with the rest of my groceries? If I do that 1,000 grocery trips in a row …
- spending 30+ minutes per day reading the highest quality material I can find; taking notes; and figuring out ways to implement the knowledge and ideas I gain --> …
johnfn
This is a good one. What's gonna happen if I respond to comments on HN for 1000 days in a row? Uh oh.
itsmevictor
I like your approach to relating your daily choices to your broader life goals.
I think you'd like Atomic Habits [1] if you haven't read it already.
[1] https://www.amazon.com/Atomic-Habits-Proven-Build-Break/dp/0...
rickcarlino
Git bisect. For certain classes of software regressions, it makes life easier. Many people (me) don’t know this feature exists and end up reinventing the wheel on their own. https://git-scm.com/docs/git-bisect
koolba
Whenever people try to argue that small and meaningful commits do not matter, I introduce them to git bisect. I’ve yet to meet someone familiar with it that does not agree.
sureglymop
Similar feelings about git worktree. Being able to check out multiple branches at once without having to deal with stash is a game changer.
benreesman
And interactive rebase. Master interactive rebase and reflog until you can do it blindfolded.
lanfeust6
Agreed with interactive rebase, but what of reflog? I've checked that for commit hashes when things have gone very wrong but I don't know many commands.
lanfeust6
Very useful. What we always say after the fact is "we need more tests".
bravesoul2
Make use of L1 wetware cache by learning how to do common things and dont make AI do them.
vouaobrasil
I only learned this in the last five years: do less, automate less, do more by hand, and use the limited capability of the manual method to really choose projects that are worthwile, rather than aim for maximum efficiency.
juliansimioni
Similar to this: if you want to optimize your productivity*, do so on a timescale of at least weeks if not months or years.
Simple example: Can you get more done working 12 hours a day than 8? Sure, for the first day. Second day maybe. But after weeks, you're worse off in one way or another.
It's easy to chase imaginary gains like automating repetitive tasks that don't actually materialize, but some basics like sleep, nutrition, happiness, etc are 100% going to affect you going forward.
* I actually hate that word, and prefer saying "effectiveness". Productivity implies the only objective is more, more, more, endlessly. Effectiveness opens up the possibility that you achieve better results with less.
01HNNWZ0MV43FF
Always fix errors in reverse order, from the bottom of the file to the top. That way the line numbers don't change as you go.
zappb
Writing tests first is a good way to end up with testable code. If you skip that, retrofitting tests is incredibly difficult.
atomicnumber3
While it can be a useful forcing function, I find it also just fits into a higher velocity workflow in general, one I would describe like so:
1. Make PRs small, but not as small as you can possibly make them.
2. Intend to write at least one nice-ish test suite that tests like 50-80% of the LOC in the PR. Don't try to unit test the entire thing, that's not a unit test. And if something is intrinsically hard to test - requires extensive mocking etc - let it go instead of writing a really brittle test.
3. Tests only do two things: help you make the code correct right now, or help the company keep the code right long term. If your test doesn't do either, don't write it.
4. Ok - now code. And just keep in mind you're the poor sod who's gonna have to test it, so try to factor most of the interesting stuff to not require extensive mocking or shit tons of state.
I've found this workflow works almost anywhere and on almost any project or code. It doesn't require any dogmatic beliefs in PR sizes or test coverages. And it helps prevent the evils that dogmatic beliefs often lead you into. It just asks you to keep your eyes open and don't paint yourself into a corner, short term or long term.
AnimalMuppet
One more piece - if the test would be hard to write, use that to drive you to clean up the architecture of that piece of code.
ryoshoe
Even if you aren't going to do the complete test code just writing down the expected checks for each test makes things so much easier
Every week for the last 3 months I’ve learned a new trick when it comes to getting whatever LLM I’m using at the time to produce better output. That’s my trade, but lots of HNers have more interesting trades than that.
In my case, only recently I learned the value of getting an LLM to write and refine a plan.md architecture doc first, and for it to break that doc down into testable phases, and then to implement phase by phase.
Seems obvious in hindsight. But it took too long to learn that that should be my approach. I had been going phase by phase myself- no overarching plan.md for the LLM.
What Trick of the Trade took you too long to learn?