No one is right all the time, not even you. Even if your parents let you think you were never wrong and your best friend in elementary school let you win every argument, real life means being wrong some of the time and maybe not having to win every argument. There will be times that no one wins, when its better just to walk away rather than fight for hours or even days. And if he’s right, give him the satisfaction of accepting it. After all, maybe the next time you’ll be right, and won’t you want him to acknowledge the win?