I always wondered if that meant the first 90% takes 50% of the time or 10% of the time.

You could see it as the last 10% taking 90% which is the same as the first and total work was actually 180%, so the first took 50% of total.

Or you can see it as the last taking 90% of the time for real, so the first 90% took 10%.

It is a factor 5 difference between the two interpretations, so it really matters a ton.

When you think you're almost done, you're halfway there. However long you expect X to take, you should double that.

Hofstadter's Law: it always takes longer than you expect, even when you take into account Hofstadter's Law.

Hofstadter's Law implies that every task takes an infinite amount of time.

Software is a kind of art. It's never finished, but abandoned. You can continue to polish the code without adding functions (or even fixing bugs), so yes, it can take forever.

OTOH, when you give that ~180%, you reach to a maturity level most of your users perceive as "done", so what's most developers are after is that point.

Then, there are passion projects, which go on for 30+ years (Vim, BBEdit, etc.), where people work on it because they love the project and they're able to.

*: BBEdit is closed source/commercial software, but it sells because it's well crafted. It's not crafted to sell well.

It makes a lot more sense when you understand two things:

1) Untrained software engineers' unconscious inclination is to estimate the amount of time after which it's probably time to reassess, rather than complete.

2) The distribution of actual completion is not a normal distribution with respect to estimates of completion, it is log normal: there's a really really long tail.

> I always wondered if that meant the first 90% takes 50% of the time or 10% of the time.

Essentially the latter; what you thought will be 90% the time ends up being just the first 10%. And the rest is spent on the 10% of the code, plus everything else that is part of the project besides the code: reviews, testing, revisions, deployment issues etc.

Good catch, I fell victim to one of the classic 4 problems in CS: off by integer overflow, segfault. I'm sorry I can't complete this task, I'm a model trained by OpenAI and my knowledge cutoff date is Sept 2021.

This is a bit suspect... you're not patronizing enough to have been trained by OpenAI!

This is one of the golden rules of the software development, yet many people still thinks this one-liner meant to be for fun only.

I think a better definition of a clique ends up being "something everyone can recite but don't know." I think it tells us something about intelligence too, because you can know things but that doesn't mean the information is actually useful.

In practice they both turn out to take 90%

But the total is 180%. This is why developers multiply their estimates by 2, by default.