Think About What You Can Do.

It is really, terribly, easy for me to think about what I can't do, and put my energy into excuses, rationals and even highly nuanced critiques so that I don't actually have to produce anything.

It is much harder to produce stuff.  One way to get over the ledge into the production "zone" is to aim at the "low hanging fruit" and do what you can do first.  That provides a base, and some specifics, which will help you move to the more complicated stuff.