Have you ever heard yourself or someone else say, "I know what I SHOULD do, but I don't!" Don't be shy. It happens. Despite what many people will tell you you're not doing anything wrong at all.
Hearing the word "should" in what someone is saying is actually hearing the words "won't happen". They might think they are going to do it, hope they are going to do it, even desperately want to do it, but if it was actually going to happen they would have said "when" or "will" or something like that. In English you can say that "should" = "will not do it."
Now before some of you protest too loudly, let me add that I don't think this is bad. What you think you "should" do is actually unlikely to be correct. It may seem counterintuitive to respond this way, so give me a chance to offer two examples to see if I can make this clearer.
First, think about a time when you didn't stand up for yourself and you thought "I should have really given them a mouthful!" To be accurate, and honest, no you shouldn't have. This "should" is more of an overreaction than anything else, and is probably even more inappropriate than the original response, because the police didn't really need to be involved and you didn't want to contribute to the cash-flow of lawyers and mediators. What you did in the first place may have been inappropriate, but adding a "should" alternative often just gives you two inappropriate choices for that situation.
Maybe this is too extreme an example for you, but I'm wanting to make the point more obvious. Even in lesser instances this is still a common type of "should" that people use and it's worth pondering how much of this is happening in any particular case.
Secondly, a "should" can be something that we learn from someone else at some time in our life, and then keep for ourselves from then on.
As we grow we are hopefully cared for by enough people from parents and teachers, to friends, extended family, professionals, and yes even doctors, to get a wide variety of suggestions about how we might best live our lives. The sheer variety of opinions alone might make you suspect that they can't all be right. It's not even enough to pay attention to the advice that is given most confidently, because no matter how confident someone else is in their convictions it still may not be suitable for you in any given situation.
When you notice this type of "should" then you don't need to persist with it unswervingly. Instead you can take a moment to stop, and reexamine the original information to decide how relevant it is to the particular situation you are considering. Even if it had value before, it might not apply so well the next time, and might need to be adjusted.
Either way, when you hear yourself say "should", realize this means you won't, and you might be better off anyway. These two self-reflections alone may help you get rid of a whole lot of "should"s in your life, and a whole lot of guilt as well.