I found myself wishing that I was an athlete. I was almost an athlete, once. I was a gymnast for approximately 13 years. I never competed, and by most standards I wasn't even very good. But I could do more push-ups than any guy in my 6th grade class, and that was what mattered to me :)
Short answer: Satan's influence.
See, every person who has ever or will ever live(d) is special. Sometimes it feels like people just say that to make each other feel good, but it's true. Heavenly Father knows each and every one of us personally, and He loves us, too. Given that Heavenly Father is so important and well-known - there's even books about Him! And some "BY" Him, too! - I feel pretty special that He knows me personally. That's like having Katy Perry on speed dial, texting Taylor Swift constantly, and having lunch with the President on a regular basis. *Only a million times better*
And guess what? Satan wants us to be miserable. And a good way to do that is to get us to believe that we aren't special or important. So in that moment, watching the Olympics, comparing myself to Olympians was a pretty good way to make me "feel like a failure" (as my sister said while watching the 15-year-old Polina Edmunds skate waay better than we will ever be able to).
The world measures people's worth according to their athletic talent during the Olympics. But sports don't make the world go round. Kindness and common sense and education and service, that's what makes the world go round. And hard work, like at a legit job. (And lots of other things, but those are all I can think of at the moment)
You don't have to be an athlete to be a beloved child of Heavenly Father. You don't have to be the best in your field to be important. You are you, and you are a pretty awesome person to be.