Lecturing a friend for ten minutes teaches them less than one good question would.

A lecture puts your friend on defence. They stop listening about a minute in and start building their reply, and whatever you say after that lands on a closed door. A question does the opposite. It makes them do the thinking, and people believe conclusions they reached themselves far more than ones handed to them.

Next time you can see a friend making a mistake, try one question instead of the speech. What are you hoping happens, or what would you tell me if I did this. Then stay quiet long enough for them to answer properly.