That caveat makes it vey hard to find situations where NVC is valid, as it relies on the motivation of both parties. It’s not enough for the speaker to have the listener’s best interest at heart (as is presumably the case with a teacher speaking to a student); the attitude must be reciprocated as well.

This is the sort of escape clause that enables No True Scotsman-like defenses of the methodology: “You did everything by the book and didn’t get your desired result. It must be because he doesn’t actually care about you.”