The saying “It’s not the size of the dog in the fight; it’s the size of the fight in the dog” perfectly captures the little dog syndrome. Have you ever noticed how little dogs have no trouble starting a fight?
Many small dogs are terriers or a derivative of a terrier and terriers were bred to keep homes and barns free of rodents. A job like that requires an attitude which could translate into thinking they can take on a dog much bigger than they are.
It's not just breeding because there are many types of small dogs, but what happens is that small dogs are very cute and they are a little over-indulged at times, which tends to make them spoiled.People tend to let little dogs get away with more. It's not exactly the same reprimanding a poodle as it is a Great Dane.
Not socialized
Socialization is so important in dogs and Dr. Marty Becker says that because they’re so tiny as puppies, people don't always properly socialize small dogs when they're young. This means that these dogs don't know how to interact with others appropriately, which can lead to disaster for the little dog — and his owner.
Then there is the helicopter parent -- yes, just like with kids it's the over-protective dog parent that doesn't allow their dog to socialize as much for fear they will get hurt. They sit with the dog in their lap or they put them in a stroller. They swoop up the dog every time a bigger dog comes by for fear it will get hurt. Thus they are creating a scenario for trouble with their pup.The dog becomes fearful and full of anxiety. Pretty soon the dog is on an anti-anxiety drug.
Many times when a dog acts out it is because they are fearful. Noted dog trainer Cesar Millan says that when you comfort your dog while it is fearful, you just reinforce that state of mind, so your dog learns that acting fearful will earn it affection.
Instead, when your dog shows fear, you have to show calm, assertive leadership — send the message that you are not afraid, and otherwise ignore the dog’s fear. Do not show affection until the dog gives the reaction you want — in this case, calmness in the face of a formerly fearful stimulus.
According to the ASPCA, many small-dog behavior issues can be effectively managed, reduced or prevented altogether through reward-based training that focuses on fun and motivation. Most small dogs are eager to learn simple obedience and tricks for tasty treats.
You and your dog will benefit from training that teaches you how to clearly communicate with him and teaches him how to listen to you.