Being a Stafford fan(all the different types including the APBT) I absolutely agree that instinct is built in. It can be trained to be controlled but the instinct is always there(with dogs that actually have that instinct - not all Staffords do these days). Why do Staffords always bee line for the nearest other Stafford over any other breed? Because they know that the dog will most likely love to play fight at their kinda rough level. Training, socialisation, responsible ownership, knowing what to do if something goes wrong etc etc etc is what's important.