It surely was not sports. I was lousy at sports. But, of course, sports are very unimportant. I have known a lot of people who have thought that sports really were important, but they were just about all losers and themselves way below average. Children are just about the only people who can be below average because they are just about the only people whom you can force to live by somebody else's standards.
Adults choose their own standards for most aspects of life.
And the ones they choose to be important are the ones in which they are above average. Look at the early Christians being turned into animal chow in the Roman Circus for the entertainment of the mob. That is a pretty bad fate by most standards of society. They were martyrs for their faith. They thought they were among the few who really did understand the order of the universe.