Why do couples always quarrel?

Actually, there are no couples who don't quarrel. If they often quarrel, they should find the reason from themselves. Couples should not only look at each other's shortcomings, but also their own shortcomings. Then we should also look at our own shortcomings. When there is a problem, you can calm down first, and then communicate after you calm down. Who is right and who is wrong? This will avoid quarreling.