I can understand being upset with yourself when you know you can do better, but for some reason, you had a bad day and just couldn't pull it together. It happens to everyone once in a while. But, at the same time, you do need to stay grounded and remember that you work hard at what you do, and you should be grateful for everything you've been given.
And then take the case of our own Carrie Johnson, who competed in Olympic kayaking despite having Crohn's disease. Johnson finished in 8th place in the Women's 200m semifinals and in 6th place in the Women's 500m semifinals. Should Johnson be upset that she didn't make it further in London? She probably is, but I think that she should be proud. She overcame a humiliating, painful, debilitating disease to compete in three Olympic Games, not to mention all her other accomplishments as an athlete and as an individual.
Johson told the The San Diego Union-Tribune that she will probably feel "disappoinment" at not medaling but that she loves her sport and "...There's really not any other incentive."
I hope she still feels this way, and that she comes home to pursue her future endeavors with the knowledge that she competed at the top of her game, and that's what counts in this life.