Ask HN: How do you prevent documentation from becoming tribal knowledge?

I've run into this situation before where I join a team and person X begins helping me with something, then person Y comes along and says, "Oh yeah we have a documentation page for this, it's buried here."

Or a different, but similar scenario: I'll begin trying to solve a problem. I'll search the team's documentation and find nothing, but then I'll be pointed to documentation that is exactly what I was looking for. Ugh.

So it's kind of funny, I'll be on a team with a wealth of information documenting everything, but it's borderline useless since I can't find what I need when I need it, and only Joe who has been here for 15 years knows exactly how everything is laid out and knows where to point me. How do I prevent this? How can I structure my documentation so it's easy to navigate and easy to stumble upon what you need. I can't be the only one that's had this issue, right?

I guess at a higher level I'm realizing that this question really is, "What's the best way to structure documentation"?

Additionally, any tips on how to do this in Confluence? I feel like at least 20% of the problem is due to how awful it is to create anything remotely navigable in that tool.