No. I see this mistake everywhere. You're confusing "knowing everything" or "making assumptions" with "mental maps". They are not at all the same thing.

The benefit of libraries is it's an abstraction and compartmentalization layer. You don't have to use REST calls to talk to AWS, you can use boto and move s3 files around in your code without cluttering it up.

Yeah, sometimes the abstraction breaks or fails, but generally that's rare unless the library really sucks, or you get a leftpad situation.

Having a mental map of your code doesn't mean you know everything, it means you understand how your code works, what it is responsible for, and how it interacts with or delegates to other things.

Part of being a good software engineer is managing complexity like that.