Self-defense is a countermeasure that involves defending the health and well-being on oneself from harm. A person has the right to use reasonable force to protect oneself or members of their family from bodily harm from the attack of an aggressor, if the defender has reason to believe he/she are in danger.
Here are four elements for self-defense to be justified:
(1) An unprovoked attack
(2) which threatens imminent injury or death
(3) reasonable degree of force
(4) in defense of reasonable fear of injury or death.
Self-preservation, survival, preservation instinct.
Number One Rule of Self Defense is - "don't put yourself in a situation where you are likely to be attacked."