The multiplicity of casual friendships online has led to an interesting new phenomenon: Because people preferentially broadcast their successes, we tend to get the feeling that everybody else is more successful than ourselves. I don't think you can avoid comparing yourself to others; what you can do is try to keep in mind that life is a mix of good and bad, and even if all you manage to do is avoid the worst of the bad, you're doing pretty well.
Take me for example. I started university when I was 13, won the Putnam competition when I was 18, went on to a doctorate in computing from Oxford University, and single-handedly bootstrapped a successful startup. I think most people here could tell you that much about me; but I doubt many could tell you that I'm 34, that I'm socially awkward and stutter when I'm nervous, that I'm diabetic and wrestle with this life-threatening condition every day, that I'm 20 lbs overweight and due to my sedentary lifestyle have the cardiopulmonary fitness of a typical 50 year old, or that I've been dumped by every woman I've ever dated.
When you inevitably compare yourself to others, remember that there's probably a lot you're not hearing about them.