I personally draw inspiration from John Carmack. I've understood his approach to be basically just stare at your problem and ignore everything else until you make a little bit of progress. The answer is there.
This confused conviction is the real problem. There is no other you to convince. The same you that you are bargaining with to do the thing is the same you that's doing the bargaining. You can at any moment just do it.
Afterwards he had money to work on other stuff he was passionate about (rockets, VR, etc.) in his own terms.
It's much harder to draw motivation to meaningless work.
Write down the problem. Think really hard. Write down the solution.