We also have 'self' expectations. Attempting to motivate ourself by saying "I should..." causes us to feel guilty, pressured and resentful. Anger is escalated by highlighting the failure of other people to behave in the ways we want. Because "I" want it to be, it must or should be. When 'should-statements' are directed towards others, we probably feel frustrated, angry or indignant. This line of thought frequently leads to a sense of injustice and self-righteous anger and sometimes, a desire for revenge.
Example: "It's not fair"; "(S)He shouldn't act this way".
How do we behave differently?
don't use preferences as demands or commands. Writing the rules for the entire world and demanding perfectionism is exhausting, not only for yourself, but for the other person as well. "Should-Statements" are not effective. Don't 'should' on yourself.
Example: NOT
(S)He should not treat me this way. It's not fair. Say instead; "it would be nice is (s)he did it my way, however, they have a right to their style."