Every great and commanding movement in the annals of the world is the triumph of enthusiasm.

Nothing large gets done by people who are merely reasonable about it. Enthusiasm is what carries a project through the long stretch where it makes no sense to anyone, including sometimes the person doing it. Analysis can tell you whether something is worth attempting, but it cannot supply the energy to keep attempting it.

If you are working on something you feel only lukewarm about, that is useful information rather than a character flaw. Either find the part of it you actually care about and put yourself there, or make peace with doing it adequately. Save the real energy for the thing that has it naturally.