Is focusing on one thing the only way to do something well? I, for one, am suspicious of such easy answers.
Personally, I’m a dabbler. I’ve never had much luck finding my “passion” or “purpose”; my track record is so bad that I’ve just about given up on setting long-term goals at all.
Does my lack of focus make me a failure, incapable of “advance in this world”?
I don’t think so.