Without it you'd be six feet under the ground in a box or you'd be in a jar sitting on someone's mantel piece. Stress is both a negative and positive factor. Distress, negative stress, zaps our energy and enthusiasm for life. It's the stuff that we're always trying to get rid of, reduce, and avoid. On the positive side, eustress motivates and energizes us to pursue relationships, engage in projects, and accomplish our goals.
Stress is caused by any type of demand.
It's the response by the body and mind to those demands. For example, on any given day, you may find that dealing with a disgruntled customer is stress-free. Then later on, or perhaps the next day, the same situation creates much stress for you. The difference is in how you looked at it and what other situations you were dealing with at that moment. Situations or events themselves are neutral.