You’re going to make mistakes sometimes. Even when you’re being rational. But you’ll greatly increase the number of mistakes you’ll make if you allow fear, greed, and anger to determine your actions.
By having better command of your emotions and impulses you’ll stack the odds in your favor, in terms of avoiding big mistakes. This requires self-reflection and it involves being knowledgeable.
Statistics is a good example of knowledge that can help tame emotions. Because often our fears are overblown. A knowledge of statistics can expose our irrational biases.