We think we need perseverance when we get discouraged. Setbacks, dead-ends, conflicting priorities, all of these are discouraging. Too many at once or for too long, we get discouraged and doubt the endeavor.
Maybe the endeavor is not really yours. Maybe the other demands truly require more of your attention to lay them to rest, then you return to it.
"Inspiration" is snake oil offered to your lesser self, the self that wants to be on the mountaintop all the time.