The Ball
This actually relates to dogs being predators. Dogs with high ball drive - i.e. bringing it back again and again and hunting for it when lost, are actually exhibiting prey drive. The dog has transferred actions such as chasing and catching that it would use to hunt if it were a wolf. Since dogs are puppy wolves in many ways it makes sense that young wolves do the same thing with pieces of prey, fur or bones.
Getting a dog to bring it back to a person is often the hard part, in addition to getting them to drop the ball so you can throw it again. Some dogs never get it, but training your dog to drop other things and acting like an excited idiot when they bring it back will make them more likely to bring it back. Most of the dogs who really like retrieving are also big suckers for praise.
This drive is sought after by people trying to find dogs for search and rescue work, as they use the ball preoccupation to their advantage. The first few times a dog actually finds the ball, but over time the act of hunting for the ball evolves in to searching for a person.
