The fourth reason why emotions matter is they influence our physical and our mental health. Take stress for example. There is a continuum of stress, from no stress at all when you're at ease and you're calm when you're tranquil and you're peaceful--to positive stress, for example, when you're under pressure to perform at your best or when you're being challenged. Then there's distress. There's acute distress, which is a momentary distress. There is chronic stress, and then there's toxic stress, which happens when we experience stressors for a very long, prolonged period of time, and it's high-intensity. As you can imagine, the greater the toxic stress, the worse off our physical and mental health can be. What's interesting about this research also is that our mindsets around stress can influence our physical and mental health. For example, a colleague of mine did research where she had people watch videos. They were videos of people doing really intense sports. One group watched the videos and said, "Oh my goodness! That stress has got to be harmful for people." The other group were like, "Wow, look how stress is enhancing their performance." Four weeks later, people were tested, and interestingly enough, those who were in the "bad stress condition" had worse physical and mental health symptoms. In our work with teachers, what we know is that the culture and climate of schools literally influences the stress levels. We've all experienced that, right? To importantly, though stress levels influencing things like stress-related absences, burnout, even anxiety, and depression. Think about that. Our organizational climates directly affect our feelings, which in turn influence our health, and it all works in a circle. Finally, interesting research shows that our experience of more pleasant emotions can buffer against the negative impact of stress. There's one classic study-- after September 11th, college students who experienced more gratitude, who experienced more pleasant emotions, post 9/11 attacks, five weeks later, had less depressive symptoms. The message here is that we have to learn how to manage our stress carefully. We have to be careful about our mindset around stress, and we have to find a way to have greater balance of pleasant to unpleasant emotions.