What is groupthink? Why can groupthink be detrimental to effective group functioning?

Groupthink refers to the tendency for members of highly cohesive groups to lose their critical evaluative capabilities. When groupthink occurs, group members tend to be unwilling to criticize one another's ideas and suggestions. Group members also desire to hold the group together and to avoid unpleasant disagreements. This leads to an overemphasis on agreement and an under-emphasis on critical discussion. In turn, poor decisions may ultimately result, thereby undermining effective group functioning.