On disappointments

I was thinking about aspect of disappointment after someone, with whom I had exchanged about two emails, said (or rather yelled, as much as you can yell in an email) that he's disappointed at me. (I think that is first time in long, long time (or ever) when anyone says that to me.)
How can he be disappointed at me when he doesn't even know me? When he doesn't know what I wish for, what I am afraid of or what keeps me going...

Let me lighten up the definition of a disappointment a bit:

Disappointment:
"...emotion felt when a strongly held expectation of something desired is not met."

In other words this person was actually mad at me because I broke the faulty image he had created about who I am based on one cute face, one profile and one email. He didn't want to know me, he wanted that I am what he thought or wished I am. (I am rather hated for what I am than loved for what I am not.)

Doesn't this apply with all the disappointments we experience: when someone reveals to be something else we thought they just reveal that we have created a false image and our disappointment is all about being angry to the person who broke that image. Because we love our castles in the sky and our predictable lives.
It would be too much to accept the fact that you can never control anything nor know someone completely (that would be boring).