One thing to imagine might be a pain or cost curve that has multiple minima and maxima. Pain can be either a demotivator or motivator in different contexts. Pain qua fatique might indicate that a reward slope exists for more conditioning. (Edit: that is on a static or realist view; the terrain of reward and pain is probably constantly changing.)

Random tangential data point: Some animals (chickens?) can learn superstitious behavior; the first action of theirs that happens to correlate with a reward can result in one-shot learning or something.