Once upon a time, a family adopted a dog. They decided to train the dog, as these pets are naturally unsanitary and stupid. "Sit, boy!" And the dog sat, so good! "Fetch, boy!" The bored teen cashiering at the pet store had recommended a cheap, wafer-thin ping pong ball to play with, and it splintered in the dogs mouth as soon as it picked it up. The dog returned it, because it is a good dog, but they paid no mind that the ball was now broken and sprinkled with blood. What did it matter? The game was more important, of course, and that man was a professional! "Fetch, boy!" The dog, naturally fearing pain, brought back a nice tennis ball instead.
"No, you dumb dog! You can't do that, you are supposed to listen! Dumb dog!" They threw the broken ball again. The dog brought back a tennis ball, again. The family took it away, and yet the dog managed to find new ones everywhere it went. The family grew angry and started slapping it out of the dogs' sore mouth, shoving in the broken ball and cutting and scratching more every time.
Eventually, the dog didn't want to play fetch. The very word made the dog cower, whimper, growl and bite. The family wailed. "What have we done wrong? Why is he acting this way?" By this time, the dogs mouth and tongue were scarred, hardly functional - he couldn't eat. "Just eat the stupid food, you dumb dog!" They screamed through their tears, shoving the dogs' head in its food bowl in childish incomprehension. The dog ran away. The family blamed the dog for running, and learned nothing.