John,
I agree with most of the posts above: Finding your fears, breaking them down, and facing them. Keep the big, fancy things you want to buy in front of you all the time to remind you what you're working for. Keep reminders of what's keeping you going when the times get tough. For me though, I get mad at what's standing in my way.
Whenever I get upset (normally it's about finances in my household), I make myself breakdown what I'm really upset about and then get mad at whatever made me feel defeated. I don't know about you but responsibilities and obligations, whether financial or not, can make you feel very small at times. I use that anger to motivate myself to push through any fear or doubt. I tell myself that I won't let that thing, whatever it is, beat me or make me feel like I can't succeed. Maybe you need to work in a full time job for a while to realize what your real desire is. Who knows?
It might be WAY off key for some but it's what keeps me going. Hope this helps John. Keep going and don't let anything get in the way of what you want to acheive.