I can completely agree with this. I think I was framing this too much in my mind (in the context of private lessons for HOW to go about approaching the trumpet). We always can learn from others; no one is above learning, and everyone can/does/should have a mentor. Perhaps sometimes it is not needed for the mechanics of playing, or maybe that is something where at one point we can progress with just practice. Yet music is a vast, vast thing which no one person has completely mastered.