Why does an experienced programmer ever need to look anything up?

It’s useful to have reference materials to check against, or for things you haven’t worked in recently.

I don't think this is like looking up a reference. This article is a general guideline on how to be a good Principal IC, the thing you're supposed to already know if you're a Principal IC.

This is like reminding a top doctor "do differential diagnosis". Nope, top doctors already know this, it's redundant advice.

This is like reminding a good thinker they must think about things: they already know this and it's presumably how they got to the position in the first place.

That's a good point.

I think this article is a promotional piece for the author's personal brand, thinly veiled as advice for others. It's "look at what I know, and here's why you should pay me". These people love to talk about themselves.