A: "1+1=2."
B: "How dare you! That math's not fair. Everyone knows it's 3."
A: "No, sorry. Math is math. It's right there in black & white. 1+1=2."
B: "That can't be right. I disagree!"
A: "It's math, not an illusion. You can't just shout 'I disbelieve!' and make it go away."