One of the biggest causes of personal suffering is "should," coupled with a sense of fairness or guilt: Joe should not talk about me behind my back. Jane should be honest. I should love my parents even though they beat me senseless.
I'm not saying to forget about what should be or how people should behave; I absolutely believe that people should be fair and honest. I am saying, though, that "should" is more useful when it is thought of more like a road map that shows where we might go instead of like a one way tunnel that dictates where we must go. There is very little in life that turns out as it should and people often do not behave as they should (including ourselves).
If you find yourself angry or upset and saying, "He should..." or "I should...", ask yourself why. Why should things be that way? Is it because they really should, or is it because that's what you expect due to what you've come to believe? Most times the answer will be that it's just what you expect and unfortunately what you expect should be or will be simply does not match reality. And making matters worse, your anger, hurt, or guilt gets in the way of doing something to make the situation different.
Here's something you can try. The next time you feel hurt or angry, rather than being satisfied with, "She should...", instead ask yourself, "Why do I feel like this?" The answer may be something like, "Because Jane said that Sharona said something that hurt me." Then go back to the beginning: "What did she actually say?" When you have that answer, then ask, "Why did that hurt me?" Possibly the answer will be, "Because I think that means..." and you will have discovered that it was your interpretation of what was said and not what was actually said that's the cause of your hurt. Now you have the opportunity to ask Sharona, "I think you said 'x'; is that right? Could you tell me more?" When that's clarified, you then may find out that you took the comment in a completely wrong way or you may find out you were right and feel the need to do something. But you can act or not act in an effective way instead of just wallowing in hurt.
So the bottom line is: "Should" is a useful guideline but don't be satisfied with it as an explanation for your suffering. Always use reality and direct evidence. When you know as much as you can, act according to what you think "should" be Work toward the ideal instead of hoping for it to happen.