People believe in versions of people that don't exist. Placing expectation and ideals on a person, said person knows this and so play that role constantly, it can go both ways as well.
Knowing that if they break the role or expectation, the 'bond' they worked so hard for will shatter. So people pretend, so they aren't alone or shunned. Just my opinion anyways, it's probably wrong like a lot I say.
Not to say true bonds don't exist, I've never had one, but people really do remain genuine friends beyond the pretending.
Must be nice.