In the midst of the Holocaust, Victor Frankl used the human endowment of self-awareness to discover a fundamental principle about the nature of man: Between stimulus and response, man has the freedom to choose.
This freedom to choose is what Frankl called "the last of human freedoms." He discovered that he could decide within himself how his experience was going to affect him. Between what happened to him, or the stimulus, and his response to it was his freedom or power to choose that response.
Every human has this ability to choose, it is one of the endowments that make us human. The next time something happens to you, whether good or bad, pause before reacting. Think about who you want to be and how that person would respond to this stimuli.