Stress and Shape
Visualize a balloon on a string. The balloon exists in its natural shape. Now, imagine pushing that balloon through a hole that is smaller than the balloon but big enough to squeeze the balloon through it. The only way to get the balloon through the hole is to deform its shape. You can't get a square block of wood through a smaller round hole, but you can push a pliable balloon through a hole smaller than the balloon.
The significant fact is that the balloon doesn't squeeze itself through the hole. The stressor does that by distorting the balloon and pushing it through the hole. In this example, you're the stressor—the cause of stress to the balloon. The effect on the balloon is stress as it is distorted, squeezed, pushed, and pulled to get through the hole—unless it breaks from the pressure of being squeezed. This is the distinction between a stressor and stress. Stress doesn't just happen. Stress is a reaction to the actions of a stressor.
Stressors distort the shape of something. Under-inflated balloons are flexible enough to be distorted into other shapes—including balloon animals for children's birthday parties. Other objects—such as brick walls that collapse under too much pressure—aren't so flexible.
Flexible objects can adapt to some distortion, but when the force is too great, the stress is intolerable. The hose bursts, the balloon breaks, the wall crumbles. Anything can reach the point of too much pressure, too much strain, too much constriction, too much restriction. This includes the effect of too much pressure on you.
[Original Post October 5, 2015]