The following appeared in an article in the Wall Street Journal: "Last week, true to discount roots dating to 1971, Southwest [Airlines] launched a summer fare sale on domestic flights, with one-way prices as low as $49. As in the past, major competitors were forced to follow suit." Why would other airlines be "forced" to follow Southwest's fare decrease? Does your answer change if you learn that this fare decrease took place during an economic recession, when incomes and the demand for airline travel were falling? Briefly explain.