I guess the one human condition that can be exploited universally is when people lose control. We ALL lose control; some are better than others at containing their emotions. Some are masters of repression. But in general; most people have a range of feelings that will come on under stress, duress, hurt feelings and the like. Emotions lead to the older biological side of our brains taking over and suppressing the cooler rational parts of our brain.
One of the worst things to do at the poker table is lose control of your emotions. That is the easiest way to make a mistake. Mistakes are made when people don't think about all the factors that go into a big decision; they just make a decision. Big mistake. When your livelihood rests on interpreting others then you have to think through all their actions, and why they made them. How can you do that if you are not sane?
Look at the elite poker table and the players there all look like they got free samples at the Zoloft convention. Not a lot of action going on even though people are winning other people's money or tournament chips worth $1000's of dollars.
Imagine what it would take a to make a bunch of millionaires become unemotional drones? Simple, it's a learned response. They all had great victories and crushing defeats and came to the conclusion that hey, it's a lot easier if you are not fighting your emotions along the way as well. They realized it just makes more money for them if they turn it off at the door. Put another way, of all the poker wannabes out there maybe the best of them prevailed BECAUSE they could keep their emotions in check?
So if you know you can put someone on tilt - to play emotionally - then why not do it?
If you know that you can be put on tilt, then why let them do it to you?