There is no one specific cause of small dog syndrome. It can be the result of a variety of factors, including genetics, early socialization experiences, and the dog's environment. Some experts believe that small dogs may be more prone to developing small dog syndrome because they are often treated differently than larger dogs, and may receive more indulgent or permissive treatment from their owners. This can lead to the development of inappropriate behaviors, such as aggression or over-dominance.

It is also possible that small dogs may be more prone to developing small dog syndrome because they may be more sensitive to their environment and more reactive to stimuli than larger dogs. This can lead to a greater tendency to become anxious or aggressive in certain situations.

To deal with small dog syndrome, it is important to establish yourself as the leader of the pack and to set clear rules and boundaries for your dog. This can be done through training, consistent discipline, and positive reinforcement. It is also important to socialize your dog, especially if it is a puppy, to help it learn appropriate behavior around other dogs and people. Providing your dog with plenty of exercise and mental stimulation can also help to prevent boredom and reduce problem behaviors. If your dog's aggressive or dominant behavior persists, it may be necessary to seek the help of a professional dog trainer or behaviorist.