The 2 pizza rule is a guideline for deciding how many attendees should be invited to a meeting. According to the rule, every meeting should be small enough that attendees could be fed with two large pizzas.
An important goal of the 2 pizza rule is to prevent groupthink, a phenomenon that occurs when a large group's need for consensus overrides the judgment of individual group members. The rule also discourages HiPPO, an acronym that stands for the "highest paid person's opinion" or the "highest paid person in the office." HiPPO describes the tendency for lower-paid employees to defer to higher-paid employees when a decision has to be made.
The 2 pizza rule is often credited to Jeff Bezos, founder and CEO of Amazon. Bezos is known to have used 'two pizza' meetings and small project teams to foster a decentralized, creative working environment when Amazon was a startup.
Why 2 Pizzas?
Bezos' decision to keep meetings small in order to encourage productivity can be backed up by science. After devoting nearly 50 years to the study of team performance, the late Harvard researcher J. Richard Hackman concluded that four to six is the optimal number of members for a project team and no work team should have more than 10 members.
According to Hackman, this is because communication problems increase “exponentially as team size increases.” Ironically, the larger the team, the more time will be spent on communication instead of producing work.