we embrace that energy. stress is something that you care about is at stake. it happens in your brain and body that helps you rise to the challenge, when something that you care about is on the line. >> kelly mcgonigal, author of a book called the upside of stwres. her work has flipped the script on stress. >> so everyone has heard of the flight of fight response brain and body can respond. but actually, you have this whole represe whole. you fell threatened, maybe overwhelmed, go into immediate survival, you can also have a stress response called a challenge response. that's the kind of stress response that gives you courage, that makes you willing to take positive risks that really helps you perform under pressure. it's a healthy stress response. it's good for your cardiovascular system, immune system.