Someone made the comment earlier. While nothing holds true 100% of the time, I think it is a big issue with dog ownership today (even small dogs). People look at dogs as an accessory and not as the potential wild animal within. If a dog views their humans as the Alphas of the pack and they are lower down the pecking order, they will tend to be more docile and let the human take the lead in a dangerous (or perceived dangerous situation). When humans behave weakly and the dog (of any size) feels they have to take on the role of the Alpha in their pack, they will tend towards more ferocious and protective of their weak human pack members. Again, this is not true 100% of the time, but it can have horrible or even deadly consequences with larger more powerful dogs like pitties, rottweillers, and German Shepards.