Dale is trying to buy a Dr. Pepper from a vending machine. When he pushes the button nothing happens. Dale pushes the button multiple times over the course of the next thirty seconds before accepting that it does not work. Later, Dale still does not want to give up on his Dr. Pepper. He remembers that one time he held the button down for ten seconds, which resulted in him getting his drink. He decides to try this. This is an example of _______________.