I don’t have to tell you that life is not fair. You already know this. But do you really believe it?
The answer is no. To believe something is to accept it as true, which then becomes a rule of action.
Do you act like life is unfair? No. We expect people, at least, to be fair. But are they?
Sure, from a moral standpoint people ought to be fair and treat others with kindness. But other people are not under our control.
This means that people will be unfair, unkind, and sometimes cruel. We cannot control that.
But we still expect them to be fair, kind, and courteous. And so we suffer when they are not.
Expect nothing and when you get nothing you will not be disappointed. The key is nonattachment.