The difference between the first and second principles of the ten principles of economics

The first principle: people are faced with trade-offs. This principle is the premise of economics. If human beings did not have such requirements, there would be no such subject as economics at all.

The second principle: the cost of something is what you give up in order to get it, which is the famous definition of "opportunity cost" in economics. The traditional cost only represents what has been paid, and the appearance of opportunity cost can better measure the real cost between various schemes.