I would draw the difference here that a library is used by hundreds (of thousands) of people, and established across different scenarios. I don't read the boto3 library AWS provides, but I can trust them and the amount of customers enough to be certain enough that it behaves the way I expect it to. The same can't be said with code we write in silos at our workplace or at home. It simply does not have the same test bench.

Yes, libraries aren't bug-free, but they give me a reliable abstraction tested in the field. Not rarely you dig into library code if you notice unexpected behavior.

If we could rely on our LLM or colleague written code, or own code, have run through the same amount of requests, sure I wouldn't need to review it, as my confidence can be north of 99.9999% it works correctly. But we can't.

I've used libraries before, where I call the API surface that they expose based on method names and parameter types, without reading all the source. Generally those libraries don't implement my software's entire problem domain area; they tend to implement things like "CSV parser" or "HTTP server". The important code, that I'm actively reading and writing, tends to be the code around those library calls.

This is different from building a product, which you only interact with via UI buttons/CLI/etc, without reading any code to understand how it conceptualizes that product's problem domain area.

People do that latter thing, and we call them "users", not "developers".

You can use it without understanding, but this won't help you actually understand how it behaves.

I am sure OP cannot understand the Unix file API without actually reading every line of its implementations (on each different architecture)! Or any function for that matter , what does sort do?? Impossible to know without reading the source. And I’m sure after reading the source you will know every detail of how it works and will never forget it.

No, but the authors of $LIBRARY are accountable if it fails