We've all done it. You lose a hand. You bust out. You sit and stare at the screen and watch as a new player fills your seat and the game continues right along, and you wonder what you could've done to prevent this catastrophe. It's a part of poker that you just can't avoid, and a lot of times it's a part that you just can't forget. The fateful hands that linger in your mind for hours upon hours, distracting you as you start up a new game, haunting you as you go about other daily tasks, and keeping you awake at night with thoughts of retrospection running through your mind. "I should've raised more before the flop. I should've gone with my instincts, I knew I was beat. I should've bet out rather than check raise and not let him get pot committed to his flush draw." Don't pretend you don't know what I'm talking about.
The problem with these sorts of situations is that, just like any other unfortunate event in life, it already happened - it's in the past now; learn from it and move on. Sitting and dwelling on how things played out won't do any good, and neither will going on tilt and starting to play crappy. A lot of times you'll find yourself stuck thinking about hands when you did everything in your power to play correctly and maximize your profits. I can't tell you how many times I've lured opponents in just like I want to, got my chips into the middle with a dominating hand, and got sucked out on to lose in the end. Sure, maybe I could've been more aggressive and pushed harder to get him off his draw... but then I'd be missing out on all those similar situations where the chips would've been sliding my way... where playing the way I did would yield the long-term profits that I'm working for.
In other situations it may be the opposite. "Why did I open-push my pocket Queens in pre-flop with a short stack right on the bubble? I should've known that there was a chance the Big Blind had pocket Kings, played tighter, and just folded those Queens. Maybe then I could've just snuck into the money." Are you kidding me? Now you're just talking crazy.
Remember that the hands we tend to think about the most are the ones we lose, even if they're played relatively perfectly and we just get a little unlucky. Learn to make quick lessons of these hands and to put them out of mind as soon as possible in order to focus on the future hands that will need your full attention. There is only so much in poker that you can control, but there's absolutely nothing in the past that you can change... it's just the facts of life. ~ B