We work with lots of different collections of people. Internal, external. Higher, lower or peer level. Mnay we may like and others we may not. Some we like to go out for a beer with and others we simply enjoy working with. Few that we can do both with at equal ease.
Many of the groups we work with are unintentionally self-selected. People hire others that are similar to them. Either culturally similar, have similar thought processes or simply someone relate-able.
Self-selected groups often suffer from below the surface groupthink. When joining a new group we can easily slip into the existing patterns and thoughts of that group. The simple fact that we are joining the group probably means we have something in common.