1) Success is a fashion, and a very dynamic and fickle one. Opinions of success (your own and everyone else's) are constantly changing. While it might seem today others are beating you, tomorrow could be your day in the press without you doing anything differently. This should help you see how little opinions of success really matter.
2) You are in control of the fashions you choose to follow and how you let them affect you.
3) Entrepreneurship is tough, and this is one of the reasons. The feeling will never get better; you'll find the more "successful" you are the worse it gets. Learn to accept this feeling and leverage it rather than fight it.