If you have this condition in your own life, the best advice I can give is:
Do anything—even if it is mediocre.
In my case, I was working on a book, and the part that kept me stuck for six months was the cover. I had an idea, but I wasn't excited about it. Part of the reason I took time off of work was to focus just on that. Yet I never came up with a 'better idea' so I took the mediocre one and ran with it.
[For reference, my daughter,Bethany—who is close to the target audience for this book—said, "Great idea! I love the inside of the book, but I would never buy it because of the cover."]
After I submitted all of my files (including the mediocre cover that had been rejected by my focus group of one) and was waiting for the printed proof someone at work sent me a link to a website with set designs. In looking at one of the concepts, it inspired an idea for a new cover, which I was able to implement and send with the second round of edits.
Here's the thing I learned. The 'wow' part of this story isn't about the 'great cover' (which Bethany actually loved). The 'wow' part of this story was finishing the book and getting the files to the printer.
It is better to have a mediocre idea well executed than a great idea that never makes it out of the gate.
What if the key to getting unstuck is to do anything—even if it is mediocre.