Yesterday, Boy 2 was resisting sharing his treat with his brother because as he says, "He never shares with me." So I think, this is a good teachable moment, "Well, this is an opportunity for you to set a good example for him. Maybe if you you share with him, he will see how nice it was and share with you next time." Boy 1 says, "That's right, and that's why sharing is selfish."
Do you think he missed the point? Or maybe he's right?