I'm highly competitive. I trained for a 10 k and only got my time down to about 52 minutes - day of the race I finished in 45 xD
Why? Because there were people to pass! And gosh darn it, none of them were going to pass me once I'd passed them!
I have high standards for myself, but I do best when I have other people to compete against. The more challenging the competition, the better.