"Protecting the principal" is one of Buffett's most famous investment maxims.

The original phrase is, "There are three rules for success: First, minimize risk and protect the principal; Second, minimize risk and protect the principal; Third, firmly remember the first and second rules."

Buffett believes that the market is full of risks, and investing is a process of gradually becoming wealthy, which requires particular caution and the need to protect the principal to have a chance to come out on top.