Though we tend to think of stress as merely a psychological problem, it has far-reaching effects on the body, too. The stress response is intended to aid us in times of danger or strife. When we perceive a real, physical hazard, a switch inside of us flips and our bodies go into "fight-or-flight" mode.
Adrenaline rushes through the body, senses sharpen, our minds work faster and more efficiently, memory recall improves and the heart starts beating faster. All of this comes in handy when we're sprinting away from a mountain lion or fighting in a parking lot. But it's not a sustainable state of being, and it's meant only to be a short-term condition. Presumably, both a chase and a fight will end, and most often rather quickly.
In order for this stress response to exist in times of danger, we must have the ability to perceive danger. This is where the trouble comes in. Now that we're perceiving danger, we can see it in all kinds of places: the mortgage that might go unpaid, the impending layoffs at work, the less-than-appealing jerk your daughter is dating.
Few of us frequently encounter life-or-death scenarios. So, in our minds, the next worst thing takes their place. Why be built with a high gear if you never use it, right? That term paper has to be finished by morning, you have to race the meter maid to your illegally parked car, table seven is demanding a refill of their drinks and you've forgotten table three's entire order -- these aren't hungry mountain lions chasing you, but they can feel just as stressful.
What's the difference between being crippled by worry and anxiety and feeling the urge to "power through" and meet the challenge? Why would stress be bad for us, if it's a response hardwired into our design?