From Human Action — surrounding passage

Not what a man should do, but what he does, counts for praxeology and economics. Hygiene may be right or wrong in calling alcohol and nicotine poisons. But economics must explain the prices of tobacco and liquor as they are, not as they would be under different conditions. There is no room left in the field of economics for a scale of needs different from the scale of values as reflected in man's actual behavior.

“Economics deals with real man, weak and subject to error as he is, not with ideal beings, omniscient and perfect as only gods could be.”

4. Action as an Exchange Action is an attempt to substitute a more satisfactory state of affairs for a less satisfactory one. We call such a willfully induced alteration an exchange. A less desirable condition is bartered for a more desirable. What gratifies less is abandoned in order to attain something that pleases more. That which is abandoned is called the price paid for the attainment of the end sought. The value of the price paid is called costs.