Fair is Foul and Foul is Fair

That line came from the three hags in the play Macbeth, written by William Shakespeare.

I think it's about game, or whatever problem in life that requires fairness. I don't think being fair is a foul because it's the best thing about life --- being fair. But I agree with the fact that a foul is fair. It's just okay because everyone has flaws and fouls so it's a fair one.

For the example:
In a game, everyone should be fair and shouldn't do any foul.