The document discusses the 90/10 principle, which states that 10% of life is made up of external events outside our control, while 90% is determined by our reactions to those events. It provides an example of how a spilled cup of coffee could lead to a bad day if reacted to negatively through anger and blame, but may be avoided by responding calmly and without overreaction. The principle suggests we cannot control what happens but can control how we respond, so by choosing our reactions wisely we can avoid being negatively affected by the 10% outside our control.