Epictetus identifies the greatest obstacle to learning and growth - the illusion of already knowing. When we approach situations with the assumption that we understand them completely, we close ourselves off to new information, different perspectives, and deeper insights. This intellectual humility is crucial for continuous development. The most dangerous phrase in learning is 'I already know that' because it stops further exploration. True wisdom begins with recognizing the limits of our knowledge and maintaining curiosity even about familiar subjects. The beginner's mind, open and eager, learns far more than the expert's mind, closed and satisfied.