I think people say that others dont act rationally, when really they just don't understand the other person's goals and how their behaviour contributes to their goals.

If i pass up $100 to get a burger, am i acting irrationally? It depends if i'm hungry. It depends how much $100 means to me (Am i bill gates?). Its impossible to say from the outside. I'm convinced much behaviour is basically the same except much more complex with multiple conflicting priorities.