Don't shoot the dog ! de Karen Pryor
One reason punishment doesn't usually work is that it does not coincide with the undesirable behavior; it occurs afterward, and sometimes, as in courts of law, long afterward. The subject therefore may not connect the punishment to his or her previous deeds; animals never do, and people often fail to. If a finger fell off every time someone stole something, or if cars burst into flames when they were parked illegally, I expect stolen property and parking tickets would be nearly nonexistent.