For me? Trust me, I didn't want to go to college at all. I'm as lazy as they come. Heck, I have to force myself to get up and go for a run every day. I'm sitting here next to an enormous NATOPS book, an FWOP I need to memorize, and about a dozen checklists I need to practice, and I'm here on the BBS.
What keeps me going? I love the job. This is exactly what I've always wanted to do my entire life. Could I fly civilian and do WAY less work? Sure. Why don't I take the out? I'm narcissistic. Honestly, I imagine introducing myself to someone, or hitting on a girl at a bar. I picture myself saying "Yeah, I'm a pilot for Delta." Then I imagine saying "Yeah, you've seen Top Gun? I do that." As horrible as it sounds, that helps a LOT. I love my job, and I love learning this stuff, and I will never stop trying to get better, but it's a constant battle of motivation vs laziness, and I find narcissism helps. And anytime I see someone score higher than me on a test, I remind myself that I know I'm better than them, and I should be showing it, so I need to go back and work harder and study more, so that I can show I'm better.
Again, that sounds a bit arrogant and immature, but I'm at a point where I COULD skate by with minimum effort and PASS, so clinging to the arrogance is what pushes me to go for more than just passing, and REALLY try to be good.