Do you want to do it or not? If you actually want to do it you should be able to obtain some satisfaction from getting it done, however distasteful the task itself. Sometimes it's as simple as that: either realising you really do want to do it or realising you really don't and reconsidering why you're trying to make yourself do it in the first place.

But sometimes the problem isn't motivation. Sometimes it's energy. Sometimes you really do want to do it, to the core of your being, but you're just too fucking tired. That's a very different problem.