Everyone has been the victim of a miracle draw at one time or another, but honestly it doesn't bother me nearly as much as it used to. Luck's a part of the game, so if you played great and lost..well sometimes there's just nothing you can do.
What really kills me is when I lose because of my own faulty play. When I know i had a good shot to take down a pot, or even worse to win a tourney, I go nuts thinking back on the big mistake hands. I know for sure that I dwell on it a lot longer than I do when I suffer a "bad beat".
Personally, the biggest hole in my game is missing bets. I want to be able to semi-consistently bet into pots that no one wants, especially late in tourneys when the blinds become a real issue. I finished 3rd in my last tourney because of a huge hand where I wasn't aggressive enough, and an Ace high took a large chunk out of my stack when a big bet would've surely taken the pot down. I win this hand, I'm confident I win the whole thing. Live and learn...