Most adults have one or two main friend groups — usually formed in one life context (school, work, neighbourhood). When that context changes (job change, move, breakup), the entire social network can shake. Maintaining three different friend groups buffers against this.
What three different groups looks like
Friends from work (current and former colleagues). Friends from outside work (hobby groups, neighbourhood, online communities). Friends from your past (childhood, university, earlier life chapters).
Why this matters
Job changes don't isolate you. Identity isn't tied to one context. Different groups know different sides of you. If one group fades, others persist. Major life transitions don't strand you socially.
Audit your friendships — are most from one context? If yes, deliberately build relationships in at least one other domain. The work pays back over decades of life changes.