Easy--the motivation is to remove the bad taste of the loss from my mouth and go to the next one determined to do better. I'm much more motivated by a loss than a win.
Chess motivation

usually, once i go over my otb games with shredder, it's pretty clear that my mistakes were (usually) awfully bad, which tells me that i was having an 'off' weekend. i always just get back on the horse and ride. :P

We should treat losses with attention to detail. Rather than see them as a crushing defeat we must learn from them and relish the opportunity to do so. This should eliminate the fear of loss somewhat, and allow you to enjoy playing the game.
Try to maintain a healthy relationship with loss, as we will always remember our losses, but not our wins.
How do you guys keep the motivation after say a bad tournament?