My main motivation is neccesity.
If you can find another means to motivate yourself, do so. Because using neccesity as a motivation sucks. :P
I make impulsive decisions and don't let myself look back.
Fear, Deadlines, Nagging Parents. Sadly I may be an introvert but it takes outside events to motivate me to take action.
External doubt. If someone says I can't do something, I challenge it and try it.
Although to others, I seem like a successful bright student, what they don't see are my horrible organization skills/fickleness/etc. But the end product is all the same. And that's quite alright.
I don't wanna get lost in the ocean.
I start spinning around to the motion.