In a perfect world we would all deal with our issues by calmly discussing them with each other and using logic and understanding to come to a fair conclusion.
However, unfortunately this is not a perfect world and throughout your life you will encounter many people who will take out their anger and frustration on you.
Perhaps it’s your landlord insisting that he has the right to change your rental agreement even when he doesn’t, maybe it’s your boss getting frustrated when something goes wrong at work, or it might even be a total stranger who you accidentally bump into while driving your car.