The document discusses the 90/10 principle, which states that individuals have control over 90% of what happens in their lives through their reactions to events, while only 10% consists of events truly outside their control. It provides an example of how one's day can be ruined by reacting negatively to a small accident, while remaining positive and in control of one's reactions can prevent the day from being ruined. The principle teaches that focusing on responding constructively to life's challenges rather than stressing over external factors improves one's life experience and well-being.