Self-defense and the martial arts comprise a study in human nature. If you look at why martial arts were created, you can begin to understand primal human nature. Throughout time, human beings have had specific needs – food and water, sleep, shelter, defense. In our industrialized age these needs have not changed.
Attackers may have an expectation of how we will respond to an attack, based on their own self-interest of getting what they want. In martial arts, we want to redirect that expectation or change it, or not show it at all.