We wait to feel ready. Motivated. In the right frame of mind. We treat the feeling as the thing that has to come first — so the task sits there, waiting for a mood that may not arrive.
But motivation usually follows action; it rarely leads. You don't think your way into starting so much as start your way into wanting to continue. The first two minutes are almost always the hardest, and almost always a lie about how hard the rest will be.
You can act before the feeling shows up. Begin badly, begin small, begin unconvinced — and let the readiness catch up with you, which it usually does.