I know when to persevere along a path and when to let go and change course.

There's no reliable signal, which is the uncomfortable part. Hard-and-worth-it and hard-and-finished feel identical from the inside on a bad Wednesday.

One rough test: ask what you'd advise somebody you loved who described exactly this situation to you, in the same words, with the same numbers. People are far more clear-eyed about other people's sunk costs than their own.

The answer that comes back fast is worth listening to, even if you don't act on it for another six months. Knowing and doing run on separate clocks.