In a threatening situation, this burst of energy provides the body with strength and speed, to run away from the menace or strike out at it in self-defense. It's that extra energy boost that spurs you to meet any sort of challenge, to achieve a goal or accomplish a task. The body's natural response to outside events is useful on the battleground, or if you are attacked by a mugger or an animal in the forest even when you are out to win a race. For example, if your boss or teacher says something that makes you feel angry or humiliated, striking out with a punch in the nose will probably get you expelled or fired. And running from the classroom or office would be equally inappropriate.
Civilization puts people in a biochemical double-bind.
To maintain peace and order, the natural stress response must be controlled and suppressed. But the body doesn't always cooperate. When triggered by a stressful event, it automatically prepares a chemical arsenal. And without an outlet, this automatic ammunition can turn back on itself, wreaking havoc on emotional and physical health. Just about any life change is a stressor.