You build momentum by working on your project.
But not all effort is equal.
First of all: you don't want to work in a way that creates negative effects: that's akin to giving yourself negative conditioning with respect to work. If the work is painful then you'll develop an aversion to it, or some defense to manage it. On the other hand, if you work in a way that feels rewarding, work won't seem unpleasant even if it is challenging.
Sometimes you have to remember just to reward yourself for having made the effort--for having thrown down the words on the page to try and capture the thought in a coherent form.
Sometimes all you can think about is what is wrong, but if you can get the problems down in writing, sometimes solutions will start to appear.
But don't worry about starting small--or seeing apparently small gains. Momentum is like that: a lot of effort is needed to gain momentum, but, once you've got momentum the progress to effort ration changes dramatically.