"Pet" dogs and "stray" dogs - why the "toughness" difference?

Well living outside the dogs learn from each other. At first most are sweet until they realize they don't get food or they don't get good shelter from just sitting around. They realize they have to fight and work for it. From fighting and from seeing many things that other dogs do they become stronger, more confident, and in charge. They will eventually know the streets and who the new guy is. By knowing this they feel confident and strong and by fighting they gain muscle. By wandering the streets everyday they gain muscle. By eating natural food like vegetables out of someones garden or even by drinking street water it makes their immune system stronger and as they reproduce their babies are born stronger than regular well cared for dogs. My cousin has a 10 year old rabbit that has lived outside since he was little and is still very strong. Doctor said he was going to die at the age of two and he's turning 11 in two months. He has befriended raccoons, snakes, opossums, rats, and everything else you can imagine including stray cats and dogs. Not once has he been attacked or anything because he's street smart, in this case he's " backyard smart" but anyway, I guess its a way of life for them.