The most famous work of the classic of psychology Leon Festinger in a modern presentation. The concept of "cognitive dissonance" tightly entered our lives? this psychological phenomenon affects our behavior and perception of the world. People strive for an internal balance between the information received and the personal motives of their behavior - sometimes even contrary to common sense. Is the desire to reduce dissonance the most important need in the life of any person? the author proves this with the results of numerous experiments and amazing historical facts.