Stress
The stress of representing a nation will rest on your aching shoulders, and coaches at the elite level are known to be a bit fierce.
The margin of error in this sport is pretty much zero, and you can't gain weight or grow...ever.
Every single thing you do is being judged, and thousands of people all over the world will be watching you on TV, just waiting to see if you screw up.
Uhm, no pressure or anything.