"Today however, I want to say no to a bunch of things, specifically the Shoulds. You should lose pounds/inches, be quieter, be nice(r), stop taking up so much room, not wear that, not eat that, suck it in, suck it up, smile, fit in, get over it.
No, I will not. No to all of that. A deep inner voice wants to climb to the top of the closest mountain, and out here I have my pick, and scream NO at the top of my lungs. NO."-Jennifer Rowe, Fat and Not Afraid
The "Shoulds" are destructive. They are part of a huge societal effort to maintain the status quo using a tool named "normative statements." They are saying, "hey, you're deviating." But in reality, the "norm" being advanced is rarely actually a norm; it is often an individual person advancing the idea that in order to be okay, everyone else needs to be like them. They are "normal" (regardless of how close to average or the majority they are) and if people are allowed to be "abnormal" (relative to them), then it suggests they might actually be abnormal. Of course behind every normative statement is the assumption that abnormal is a bad thing.
In other words, if someone is using the word "should," it is often entirely about their own fears. They are trying to fit in by forcing others to be like them. They are afraid that if you stand out, it will somehow invalidate them and their efforts to fit in. They are afraid that if everybody else doesn't want to be normal, they will lose the meaning normality holds for them. If they base their life and values on what they consider normal, it is vitally important to them that normal exists outside themselves.
The good news is that this is entirely about them. Good boundaries show that nothing in their motivation or words has any actual consequence for you. You can empathize with their fear, but you don't need to take responsibility for it.
Never own other people's norms.