Our experience suggests the vast majority of dog aggression begins as fear or nervous aggression, a puppy reacting to something that scares them, whether that's a new environment or another dog, by trying to make it go away with a growl or a bite. Many owners, seeing a puppy terrified of other dogs, protect them in ways that unintentionally reward and reinforce the fear, avoiding contact entirely rather than working through it. As the puppy grows, the very socialisation they need often gets avoided instead, precisely because they seem scared of other dogs. Every interaction becomes a learning experience, and a fearful puppy who barks aggressively and successfully makes another dog back away learns a clear lesson: acting aggressively makes the scary thing leave. Once that pattern is proven repeatedly, the puppy can shift from genuinely nervous to what looks like artificial boldness or dominance. The instinct to avoid all contact is understandable but usually backfires; the more useful approach is controlled exposure at a distance the puppy can cope with, working closer only as they stay calm. Counter-conditioning, pairing the sight of another dog at a safe distance with something the puppy loves, gradually changes how they feel about the trigger itself. Puppies under twelve months old are usually far easier to redirect with effective training. Past twelve months, more of this behaviour has become learned through repeated experience. Aggression often develops after a single negative encounter with another dog, which can be enough on its own to trigger this same fear-to-bold progression.