But we'll pursue things even if we know we won't be the "best" at it. For one thing, in the arts there is no "best". There are things like "favorite" and "successful", but not "best".
And in sports there are so many levels of satisfying achievement that even if there is another participant who is better, there still remains small victories like personal records. There are even those times of elation when you managed to pull together a game that bested those players and courses and games you never before defeated.
In most pursuits I suspect that it's just as Tom Waits sang, "...the obsession's in the chasing and not the apprehending; the pursuit, you see, and never the arrest"
So, perhaps it's in the not knowing if we'll fail or succeed that we find the faith to plod on and practice. We can still hope for success and we grow to understand failure as mere stepping stones that lead in new directions.