Groupthink is a psychological phenomenon that can occur in groups of people. Rather than critically evaluating information, the group members begin to form quick opinions that match the group consensus. Groupthink seems to occur most often when a respected or persuasive leader is present, inspiring members to agree with his or her opinion.
Groupthink is sometimes positive but is more often seen in a negative light, particularly in the United States and other countries that value individual opinion. Mass hysteria can be seen as an extreme example of groupthink.