Peers tend to be the people in the organization with the same specialist knowledge that we do. Often they come from a similar background and same degree of experience. They know what we know.
So when a peer has a more assertive or aggressive style than you do, or simply comes to different conclusions from the same set of facts, it can feel like a personal attack on your way of doing things. Our internal monologue oscillates between negative self-talk (“Why didn’t I think of that?”) and defensiveness (“That’ll never work anyway!”). Moreover, there’s a natural competitiveness between people at the same level in the organization – you’re often competing for the same resources and promotions.