[gmueckl]

You assume that you always have a mature option available. That's (a) definitely not a totally generalizable assumption and (b) my point is that mature options only exist because the people that developed them just did it when confronted with the task.

[kulahan]

We are specifically talking about something that does have a mature option available. That’s why it’s stupid to try and implement your own version of something complex.

If you change the story such that the product is actually needed and universally immature, of course building it is a valid argument.

Regarding b: Right, and the point of this article is that for those types of things, go for the already-mature thing. You’re arguing a point nobody is making.

[gmueckl]

I'm not changing any story here. All this "use a library" advice to juniors isn't as universal amd fast as everybody makes it sound. I always find that it sounds too discouraging. There is no magic in these libraries and in their creation - just time and effort. And that's something that needs to be mentioned, too. You can roll your own if you're willing to justify the effort. Depending on the context, it may just not be a good use of your time.

That's why it's also important to point out that no significant piece of code is mature and stable from the start, but was brought into this state iteratively using tools and processes that are available to everybody else, too. The biggest difference between existing mature code and new code under any good development process is age.