Big things are hard to do. Big things you've never done before are even harder to do. One thing that helps is to cut the big thing into smaller more manageable pieces. Another thing is to reward every little achievement of that smaller piece. I can get discouraged pretty easily as I can't sit and work on art for 10 solid hours a day. Silly bills. Celebrating small things helps me feel like I am doing something, which feeds the enthusiasm, which makes me want to do more.
I recently made a deadline for a portion of this big project I'm working on. To make sure I get something done every single day, I made a paper chain to represent every day. Then I labeled a jar with HOW I MOVED THE PROJECT FORWARD TODAY.
Every day I will take a link off the chain, write what I did for the project on it, and put it in the jar. In this way I will triumph!