The human condition is to try to overcome trauma. How affected today are most people by what happened on 9/11?

Smaller attacks, on a consistent basis, would cause more psycological damage over a prolonged period of time. I'm no psychologist though, it's merely speculation on my part and I could be wrong.

As mentioned by someone before, speaking in terms of proportional responses, the more damage you do the more damage you can expect to be done to you. Maybe that's what terrorists want, I don't know.