People have a strong confirmatory bias, which is remarkably difficult to overcome. In this research, we investigated how we could help people rectify the confirmatory bias, using Wason(1960)’s 2-4-6 task. 195 University and middle school students participated in our study, in which they were to find out the rule “increasing 3 numbers,” starting from the 2-4-6 number sequence. Prior to the task, the participants were assigned to one of the four training conditions: (1)“Counter-Examples”, in which participants were instructed to create the positive and counter-examples for the current hypothesis; (2) “Two-Hypotheses”, in which participants were instructed to create examples for two different hypotheses; (3) “Counter-Examples-AND-Two-Hypotheses; (4) Control, in which participants were told to think about examples consistent with their hypothesis. We found that the training to think counter-examples facilitates attempts to falsify the current hypothesis and subsequent hypothesis change, but creating examples for two different hypothesis did not.