We often stand in front of vending machines, pondering a very hard decision. We put our money in and push the button. Usually, we get what we just paid for, but not always. Sometimes nothing comes. We push the button again and again. Not only do we not get our selection, but the coin return isn't working either. Those most frustrating times of all are when you're desperate enough to try again, and maybe again, putting in your money - getting nothing in return.