Documentation can describe a system state, and how to use or approach it, but in my experience it really lacks in capturing the full depth of experience when it comes to interacting with it. All the little shortcuts and workarounds. All the debugging steps. Seeing something, and realising you've seen it before and solving it in 5 minutes instead of the entire day it took you last time. I could write a story about that day, but it wouldn't do anyone any good - they won't learn from that experience like I did and it won't spring to mind instantly. Assuming they even know where to find a piece written about their specific problem.
So when someone says "How do I X?" all I can think about is all the incidental things I've learned when trying to do something else. This builds the bigger picture. I can answer your question, but you'll just paste the code in and be back to ask more tomorrow. I valued the coworkers who treated such things as more of a discussion and learning opportunity than a transactional question-answer routine.