The title of the contribution sounds simple, but the closed market cycle is the cornerstone of economics as a science. Households have existed for millions of years, businesses, the market for goods and money for thousands of years, but the market cycle began to close only about three centuries ago. Through the process of bourgeois revolutions, the condition for its closure was fulfilled–the freedom of every single person. Economics “only” explains the system in which we live. Children perceive this system from an early age and wait to learn about it at school. They meet the basics of economics in civics in the 9th year of elementary school, or in the 4th year of eight-year high schools. 35 years after the “gentle revolution”, after the closing of the market cycle even in the territory of Slovakia, they still don’t learn about it. The purpose of the contribution is to help all teenagers as well as their teachers to understand the system in which they live in a simple way. It is a basic assumption of the rationality of their daily decisions.