A teacher who remembers your name five years later taught you more than the subject.

Being remembered means you were seen as a person rather than a seat. A teacher holds thousands of names and loses nearly all of them, so the one who greets you five years later was paying a kind of attention that was never in the curriculum. That attention is probably the main thing you took from the class. Most of what anybody learns about being taken seriously comes from somebody like that.

If you can name one, go and tell them, by email or in person. Be specific about what they did. Teachers rarely find out that it worked, and five minutes of your time closes that loop.