It has consistently been found that people produce more ideas when working alone as compared to when working in a group. Yet, people generally believe that group brainstorming is more effective than individual brainstorming. Further, group members are more satisfied with their performance than individuals, whereas they have generated fewer ideas. We argue that this ‘illusion of group productivity’ is partly due to a reduction of cognitive failures (instances in which someone is unable to generate ideas) in a group setting. Three studies support that explanation, showing that: (1) group interaction leads to a reduction of experienced failures and that failures mediate the effect of setting on satisfaction; and (2) manipulations that affect failures also affect satisfaction ratings. Implications for group work are discussed. Copyright © 2005 John Wiley & Sons, Ltd.