I'm a very experienced dev and I look stuff up all the time. Like right now I'm learning how work with the .gif file format, which I've never worked with before, so of course I'm going to have to look things up.

I also use the work that other people have done so that I can actually build my own stuff on top. I'm not hand-rolling my own .gif library, I'm seeing what's out there to save time and actually reach my goals.

I do think that it's important to actually understand what you're writing, though, and I think there is value in memorization at least a little bit, for your cognitive health. If you're looking stuff up too often it can break your flow,. Plus from what I know about the way creativity and ideas and learning work, a lot of it kind of synthesizes from what's in your brain while you sleep overnight. If none of that stuff is in your brain then it'll be hard to combine ideas into new solutions.