Why Am I Always Disappointed in Others?

My theory:

I like others to treat me how I treat them, but this almost never happens. Why? I expect everyone to treat me highly.

As a consequence, I treat everyone else highly. But is this reasonable?

And perhaps why I’m always disappointed in others is because I expect them to treat me how I treat myself, because I have such a high expectation of myself? And I feel disappointed because I don’t see others as high as me?