I want to believe that it's almost always the fault of the owner since I have known incredibly sweet pits and rotts, but there is a part of me that has to disagree. I am a good dog owner. I love my dog more than anything and she is like my baby. She is incredibly loving to me (98% of the time) and about 10 close family/friends. However, this is the dog who will terrify anyone who comes to the door, she has attacked more strangers than I care to admit (bit one last week), and can be a vicious dog. Luckily she is a chihuahua so I really have very little to worry about in terms of her killing someone. I have had her since she was probably 8 weeks old and I'm convinced she was just born evil. Some are, some are not. I wish I could say otherwise.