Luckily, we had rules and continuously consulted with individuals that we respect prior to making investments decisions. This enabled us to check our emotions and kept us observant. If you have rules, and then have to justify your decisions to knowledgeable colleagues, it has a tendency to keep you rational. The other tendency one has is to want to use leverage to increase your earnings. Leverage is when you borrow money to use to invest with.
Casinos also extend credit.
Brokerage houses make more money when you invest more money. Leverage also has the tendency to increase your loses. Leverage is only appropriate when you can afford the additional risk associated with its use. Let me just put it simply, human nature does not promote good, consistent investment strategies. Only self discipline and knowledge can protect you.