The pressures are too much. They hear it all and see it all. They have to steer their life among these and reach the shore safely and it is sure a difficult ride. Add to this the hormonal and physical changes taking place in their body they sure have their cup full. They are terribly conscious about themselves and desperate to make a good impression.
Every minor flaw gets magnified and many even develop a complex about it.
I remember agonizing for years over my nose which is slightly on the larger side till I realized that no one really noticed it. That s the way it is. Teenage turns everyone into compulsive worriers. I once had a friend who even worried cause she had no problems. She was sure that there was something wrong with her.