I’m not a generalist. No one is.
I don’t suffer any delusions of being a world-class composer or arranger, but I know that I have specific knowledge that makes me effective in specific situations. I can write for my own groups better than almost anyone else, because I know exactly what will work for the Aces or Shades of Blue.
I’m not a world-class conductor, but I know how to get the best out of my own students, because I know them personally, and have developed specific skills that work for the students I regularly work with.
I’m not a Pulitzer Prize-level writer, but I know how to write something daily here that illuminates a small idea, and expresses my personal viewpoint, clearly and succinctly.
I’m not Dad of the Year, but maybe I’m specifically good at being a dad to my own kids.
All knowledge is specific. You might not even be aware of how specific it is, until you step back and consider how your knowledge is shaped by your situation.