Almost all our observation of others makes the exact same error. We make sense of others' behaviors as if they understand things the exact same way we do. So our understanding of their faults and their comely behavior is as if it is motivated by the exact same thing that would motivate us to behave that same way. I have found this to be true even of a great number of young psychologists.
It rarely occurs to us that all of us, myself included, distort our perceptions. As a result, the vast majority of our "wrong" behavior is often the proper response to what we perceive. People who are hostile perceive the world as out to get them; anorexics see themselves as fat; productive people see the unproductive as lazy, and so on.