This reminds me of an article I read where mountain rescuers talked about the dog they took with them to help finding people:  if the rescue party was unsuccessful in finding anyone, no matter how exhausted they were when they returned, the last thing that they had to do was to "hide" something for the dog to find, to give him the feeing of having succeed in the mission, to make him feel useful, and to keep up his spirits so he wouldn't be depressed that he had not achieved the goal.