A good tip would be to try and focus on the stuff you may be able to alter. Comparing against others can cause some bad feelings. Everyone is at their own pace. Comparision is good if you use it positively where you see something you like, try to incorporate the change if possible. Successful can also be a tough term because the way society uses it. Take a look at your accomplishments, these are successes

Not trying to blanket term or dismiss how you feel, just some info that may cover reasons why. I don't mind a pm if you want advice