The 90/10 Principle states that 10% of life is made up of external events outside of our control, while 90% is determined by our internal reactions to what happens. How we react to situations like spills, traffic, delays, and setbacks largely influences our experiences. Applying the principle means not letting negative reactions to small uncontrolled events affect our mood and entire day. Instead, responding calmly and positively ensures the external trigger does not ruin our experience or relationships. Understanding and applying this principle can change one's life by gaining control over reactions and avoiding unnecessary stress.