We know that exercising specific muscles causes them to grow stronger and that practicing physical skills like tennis or golf can help us improve those skills and make some of the movements familiar enough to be automatic. We also know that regular practice of cognitive skills such as reading, writing, arithmetic or languages make us more proficient at those skills and "smarter" in terms of those valued abilities. When it comes to emotions, however, we don't usually think of practice leading to proficiency despite the fact that such practices have been around for thousands of years in the form of yoga, meditation, and various forms of prayer.
Most of us are familiar with the stress emotions of anger and fear, the fight or flight response, and the physical and mental costs of living a life with too much stress. But until we begin experiencing symptoms of accumulated stress, we seldom take to trouble to find out what we can do about it. Several programs for mindfulness based stress reduction came into being as training for people after they had already experienced their first (stress induced) heart attack. Patients who were highly motivated discovered that they could fairly quickly learn techniques to reduce chronic stress in measurable ways.
It turns out that we have a mechanism for arousal of the fight or flight mechanism AND a mechanism to turn off the fight or flight emotions so that we can rest and recharge, thereby saving our energies for the real emergencies. But the triggers for fight or flight are built for emergencies and operate instantaneously without our having to think about them, so that we don't hesitate in a life or death situation. And the memories of dangerous situations get and hold our attention so that we are less likely to let dangerous things sneak up on us. As a result, we can naturally learn to maintain a mental and emotional state of high alert by anticipating dangers that are still far off. Some dangers may be memories of a past situation that no longer exists, and some may be imaginary anticipated dangers that will never come to pass. Yet they all trigger the powerful fight or flight responses that we associate with a stressful life on the edge of catastrophe. And we learn to stay on high alert by practicing this state more and more. If we accidentally strengthen our stress response by practice, then it is possible that we could intentionally strengthen our relaxation response by practice, thereby giving us a healthier emotional balance to our lives.