Fans of each team watch the same tackle and see two different fouls. Loyalty edits the footage.

Wanting your side to win does not just change the argument afterwards. It changes what you see while it is happening, which is why both sets of fans are honest and both are sure. The editing happens before you get a chance to be fair, so being fair takes a second pass.

Watch yourself at the next game. Notice whether you only replay the calls that went against your team, and whether you have ever once said a close one looked right for the other side. That small admission costs you nothing and it keeps your eyes working.