My daily experience suggests that this happens primarily when the developer isn't as good as they assume that they are at expressing the ideas in their head into a structure that the LLM can run with. That's not intended to be a jab, just an opportunity for reflection.

But the moment I got the idea in my head, is the moment I got the code for it. The time spent is moslty checking the library semantics, or if there’s not some function already written for a specific bit. There’s also checking if you’re not violating some contract somewhere.

A lot of people have the try and see if it works approach. That can be insanely wasteful in any moderately complex system. The scientist way is to have a model that reduce the system to a few parameters. Then you’ll see that a lot of libraries are mostly surface works and slighlty modified version of the same thing.