If you have four apples and three hungry people visit your fruit bowl, how many will you have left? Probably, because real life does not always follow a mathematical model, you'll have none. Some greedy person will eat the one remaining. Humans are not intended to live their lives 'by the numbers'. We have to do our best to keep track of resources and live within our means but we also have to be spontaneous. If your bowl is now empty, it can mean only one thing. A new delivery of fruit is going to have to come from somewhere! Stop worrying and counting.