The 90/10 Principle states that 10% of life is made up of uncontrollable external events, while 90% is determined by our internal reactions to what happens. Two scenarios are presented where a spilled cup of coffee starts both days, but the reactions differ greatly, leading to very different outcomes. While we cannot control what happens, we can control how we choose to react, which largely dictates whether the event will negatively or positively impact our day and relationships. Learning to react properly by not letting negative comments or events get to us is key to applying this principle to reduce stress and improve life.