Keep going when the work becomes routine enough to stop flattering you.

Early on, the work flatters you. Everything is new, every session produces visible improvement, and you get to feel capable. Once it becomes routine it stops giving you that, and you have to continue without the pleasant sense of becoming something. Most people leave at exactly that point.

Notice if your interest fell away just as the work stopped being complimentary. That moment is not a sign the thing is wrong for you. It is the transition from novelty to actual competence.