This is something I've struggled with as a writer for decades; staying motivated. Motivated to write, motivated to imagine. When it strikes me, it usually does so with a vengeance and I'm able to conjure ideas and scenarios to the point that it excites me to have such creative control over whatever world I create.
I imagine this experience of being overcome with inspiring creativity to be not unlike that of people who claim to be divinely inspired, as if to provide a mode of dictation for the word of god. Even more so due to the fact that I've never been good at hanging onto that motivating inspiration, and thus I have to fit as much into it as I can before it goes away.
Once it's gone, everything I feel towards a project seems as if it goes into a kind of pause - waiting for the next wave of motivation, which may or may not come. Therefore it sits on a shelf, slowly rotting away - it becomes a race between the arrival of the next wave of inspiration and the deterioration of the original concept.
If I try to force myself to create and become motivated and inspired, I find that it actually works against me. Like trying to smooth rough water with a flat iron, or like trying to force yourself to fall asleep - it just makes the original problem worse.
But music helps.
I've found that if I'm able to find the right tunes that put me in the mindset I need to be in to work on any particular project, I can actually truck through it much more smoothly. In fact, this has been the case for me since I was a kid. When I was 10 years old, I and my teachers discovered that by simply letting me listen to headphones during schoolwork hour, I was able to get it all done, where before I was barely interested to even do it at all. Not because I didn't understand it - I just wasn't interested, it bored me.
These days, I've found that - depending on what I'm writing - I can go to Soundcloud and look up the tag "film score" or "soundtrack", and find music from relatively unknown artists who create some amazing work. In fact, for my screenplay I've been able to secure the rights to a track I found there that was composed by a guy from Buenos Aires who went to Berklee College of Music in Boston. I listen to this one a lot.
In the off-time, however, I have a hard time coming back to my project as much more than "just another thing that's on my plate". So, writers - how do you stay motivated? How do you keep your project on the forefront of your mind without turning into another chore you've given yourself? That last question is not to imply that I don't love what I'm doing, because I do. But my love for it seems to have little to do with whether or not my motivation to do it sticks around long enough for me to complete it.