After you've been objective about what you like and don't like about yourself, perhaps you'll arrive at the conclusion that for the 95% of hang-ups you can't change, there's a small 5% that you can change to make yourself feel better.
Go ahead and fix yourself some objectives (realistic ones, mind). You're never going to develop a tall, willowy figure if you've always been short and curvy, but if shifting a few pounds will help you feel better, do it!
The same goes for your job. Even if you're not going to win Manager of the Year, nothing is stopping you from asking for a meeting with your boss to discuss your career prospects. Instead of falling into an "I'll never make it" attitude, get stuck in and make progress. Quit your 'all or nothing' reasoning!