Have you ever gotten stuck on a project?
Maybe spent a few months where you didn't work on it at all?
And what do you do then? Do you just give up the project? What if that project is your dissertation or thesis? Or your masterpiece? Or even some smaller project that you were enthusiastic about until other issues demanded your attention?
If you're stuck and you want to get moving again, all you have to do is start. And be patient. It can be hard to reorient yourself to the task. And it may seem like the project doesn't move at all as one obstacle after another appears.
But if those obstacles are what stopped you before, then you need to find a way to move past them if you want to finish your project. You don't necessarily need to know exactly how you will accomplish your task, or how those obstacles will be overcome to accomplish something.
Goethe said, "Whatever you can do, or dream you can, begin it. Boldness has genius, power, and magic in it." So begin. Once you get moving again you can reconsider the obstacles and how to approach them.
But the key is to get moving. Get yourself used to working on the project. Get yourself used to putting in your time. The momentum that you gain by engaging with the problem rather than putting it on the back burner is deceptive: you start off slowly, but once you have built the momentum, it is possible to maintain it with less effort.
Only by starting again, by can you finish the project.