The most common case, and the most delicate. You are not playing to be right: you are playing to reach him without pushing him away.
Before you play: be honest with yourself
When someone close to you proudly announces a “discovery” that shakes your faith, what is your very first reflex: to correct him, or to listen to him?
Your answer already shapes what follows. Here, you are not playing to be right, you are playing to not lose him. Listen first; a good question is worth ten arguments; keep the bond before the victory.