I'm an artist as well as a programmer. It looks like one of the things you're not appreciating is the sheer size of most commercial codebases. It's not possible

I'm an artist as well as a programmer. It looks like one of the things you're not appreciating is the sheer size of most commercial codebases. It's not possible to keep it all in your head, or even scribble meaningfully about it in a notebook. It's barely possible to keep the bare minimum you need in your head, and that can take a while to build up -- and then poof, it's (somewhat) gone because your coworker can't Google a simple question. If it was just the size, it would actually still be manageable with a notebook -- but it's not just size. Every single character on every single line matters, to some non-negligible extent. If you could condense that into a notebook, you'd condense the code in the first place. Imagine you (and your ancestors) had written five hundred novels. Now you're making a significant change in the storyline. You need to be DAMN SURE you didn't miss anything anywhere, or created any plot holes. You can either take a million notes as you go, defending against all possible interruptions, taking obscene amounts of time; or just try and focus and get it done. What would you do?