Experts hoard, leaders teach

There's a difference between an expert and a leader. An expert can hold onto what he knows. A leader teaches it to everyone else.

If I'm truly going to be a leader, that's the work—not just knowing the thing, but handing it down so others can carry it too, and lead by example. And here's the test of whether you actually understand something: can you explain it to a six-year-old? If you can't, you don't understand it yet.