Stress is to refuse to accept a circumstance in your life to which you have no control. Stress is measured by the amount of energy that you invest resisting those circumstances. Stress is to waste energy attempting with your thoughts and feelings to change a person, an event or a circumstance around you.
The trick to avoid stress is to realize that no amount of effort can ever change the circumstances while they are happening to you, no matter how bad. Do no oppose the moment, instead accept and feel what is occurring.
--Thanks to Arsalan bhai for his above comments