Make a fist and squeeze it tight. Keep squeezing—as hard as you can—while you count to 10.
What happened to your breath while you did this? Most people find that they completely stop breathing, which is what typically happens when we're under stress. If you think about it, this response makes sense. The body seizes up in a mild form of shock.
But this response is exactly the opposite of what is healthy for the body. Instead of seizing up, we must learn to relax during times of stress, for only when we're relaxed can we find a solution.
Yoga can help you practice this principle in action. In yoga, the "stress" is the physical challenge of the posture. Although our first response to it may be tension, over time we can learn to deepen our breath and expand into the pose.