Motivation ebbs and flows. It is fickle and short-lasting.
So we can't wait for the muse to compel us to work. As Chuck Close said, “inspiration is for amateurs.”
However, what we can do is develop a passion for something and use it to solidify our grit. Having a little excitement helps us push through crap (criticism, rejection, assholes, and pressure).
If pertinacity and practice are a powerful combination, then discipline is true freedom. We are nothing without planned intent.
The fight is already there. The rest is permission, one that we can only give ourselves.