You shouldn't have an aggressive animal.
Sally is looking at dogs at an animal shelter.
Sally wants to adopt a pet.
Sally adopts a beagle.
Sally adopts a pit bull which, due to its naturally violent tendencies towards other dogs, kills a pug at a dog park.
The beagle brings Sally years of enjoyment and companionship while in turn receiving proper care and health.
The pug dies, Sally feels blame and responsibility, the owner feels grief over the owners loss.