Groupthink is a psychological phenomenon that occurs within a group of people, in which the desire for harmony or conformity in the group results in an incorrect or deviant decision-making outcome. Group members try to minimize conflict and reach a consensus decision without critical evaluation of alternative ideas or viewpoints, and by isolating themselves from outside influences.
Loyalty to the group requires individuals to avoid raising controversial issues or alternative solutions, and there is loss of individual creativity, uniqueness and independent thinking. The dysfunctional group dynamics of the "ingroup" produces an "illusion of invulnerability" (an inflated certainty that the right decision has been made). Thus the "ingroup" significantly overrates their own abilities in decision-making, and significantly underrates the abilities of their opponents (the "outgroup").
Doublethink is the act of ordinary people simultaneously accepting two mutually contradictory beliefs as correct, often in distinct social contexts. Doublethink is related to, but differs from, hypocrisy and neutrality. Somewhat related but almost the opposite is cognitive dissonance, where contradictory beliefs cause conflict in one's mind. Doublethink is notable due to a lack of cognitive dissonance — thus the person is completely unaware of any conflict or contradiction.
George Orwell coined the word doublethink in his dystopian novel Nineteen Eighty-Four (1949); doublethink is part of newspeak. In the novel, its origin within the typical citizen is unclear; while it could be partly a product of Big Brother's formal brainwashing programs, the novel explicitly shows people learning Doublethink and newspeak due to peer pressure and a desire to "fit in", or gain status within the Party — to be seen as a loyal Party Member. In the novel, while to even recognize, much less mention any contradiction within the context of the Party line was akin to blasphemy and subject to possible disciplinary action. More certain was the instant social disapproval of fellow Party Members.