A more thorough explanation:

The hypothetical-person defense is a legal defense used by a defendant who claims that an undercover law-enforcement officer or someone acting on their behalf encouraged them to commit a crime. The defendant argues that they were convinced that the conduct was not prohibited or that they were persuaded to commit the crime.

This defense is only recognized by a few states and the Model Penal Code. It is also known as the objective method.

John is a drug dealer who is caught selling drugs to an undercover police officer. John claims that the officer encouraged him to sell drugs and made him believe that it was legal. John argues that he would not have sold drugs if the officer had not encouraged him.

This example illustrates how the hypothetical-person defense works. John is claiming that the officer persuaded him to commit the crime and that he would not have done it otherwise.