Depends how familiar I am with what I'm doing. For something like a simple React component, I don't need to look up syntax. I've done it a million times so that's committed to memory. But, let's say, Rust... I'm just really starting out with it and have to go to the docs to see how to do even simple things. I'd also add, sometimes my brain just refuses to work with me.
Example:
I was super tired and trying to filter an array. I tried doing
.filter({ name: -1 });
instead of:
.filter(node => node.name - payload.name);
It really just depends. But it's super normal. (Though, I don't know how you define "experienced programmer" so my opinions may not be applicable)