Act IV, Scene 3

            In Act IV, scene 3, Malcolm and Macduff meet in England, where Malcolm tests the loyalty of his new recruit, Macduff. By negatively speaking of himself and declaring himself a greater tyrant than Macbeth, he hopes to bring out Macduff's true colors. His attempt at reverse psychology takes its effect, Macduff is thrown into a fit of anger against the "untitled tyrant" Macbeth, and Malcolm enlists his help in the struggle. Reverse psychology is getting somebody to do something you want by suggesting that they do the opposite. This works better when the other person is worked up and making emotional decisions rather than thinking things through (Straker, 3). A common form of reverse psychology is to forbid an action. When you say 'do not X' you are also implanting the suggestion to do X. If they say they will do something, you can express doubt that they will do this. They then have to assert they will do it (and then actually do it) to prove you wrong. If the other person is likely to believe you will use reverse psychology, you can go for a reverse-reverse effect by suggesting what you want them to do, but perhaps in an oblique and non-obvious way. In this scene of Macbeth, reverse psychology works in favor for Malcolm. 

Straker, Richard. "Reverse Psychology." Reverse Psychology. 4 June 2012. Web. 13 Nov. 2015.