As Brendan Murphy points out in this article, we are not always in control of what happens to us, but we can control how we react in any given situation. While our thoughts and emotions can get away from us, we can learn to step back, observe, and then choose the perspective we want to take at that moment. We can also learn not to continually replay unhappy and troublesome events long after they’ve happened. We can learn to be in control of our thoughts and emotions and lessen the stress in our lives.
http://tinybuddha.com/blog/who-thinks-my-thoughts-steps-on-the-path-to-mindfulness/