[quote=@DarkwolfX37]
<Snipped quote by Balance>

The other answer, by the way, is what you're getting towards. It's that every human has an existentialist need to believe their surroundings as real. We interpret our surroundings and consider our interpretations as our surroundings, so we believe what we believe to be real instead of what we believe. Two realities don't mix easily, and there are a lot more than two people. Ergo, fighting.
[/quote]

But then you have the same problem: there's a lot of missing steps between "two realities don't mix" and "fighting".