WTF?!

I have a great life - amazing family and friends, stable working life, enough money to get by on, and I'm pretty smart, if I do say so myself. But I can't help but feel like I'm a failure. For some reason I always feel like I'm not good enough for someone somewhere, and that brings me down. I feel stupid for feeling so depressed for no reason! I feel like I'm exactly the kind of person I can't stand - an ungrateful asshole. But the thing is, on the outside, I'm sure I seem perfectly normal. God, I'm either really messed up or my puberty hormones are still at it at age 23.