Alan needs some extra income and decides to offer massages at the mall. He quickly finds stiff competition and gets into a price war with another masseuse. The price war eventually gets so low that the entrant decides to exit the market.
Price wars aren’t good for business profits, which is why many firms may want to collude. If two goods are close substitutes, prices should be driven down near the marginal cost of production. This is a good introduction to the long run outcome of perfect competition, but can also be used to show the shut down rule. When prices drop too low, it may be worth some firms to stop production.