I'm working through a jazz guitar course focused on bebop vocabulary and every day we're instructed to improvise for 15 minutes over a given set of chord changes we're studying.

The first couple of days it was novel, so it was easy to get motivated. By the 3rd or 4th day I began to feel like "I've explored everything that can be done with these changes; this is pointless." yet I pressed on.

Turned out that almost always I came up with something that surprises me.

I now focus on just doing it, regardless of how 'inspired' or motivated I feel.