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.

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’...