It's typically invested in securities such as the stock market. If the market value of those securities takes a nose dive, so, too, will the cash value of one's

It's typically invested in securities such as the stock market. If the market value of those securities takes a nose dive, so, too, will the cash value of one's life savings. Market value is driven by supply and demand. If, for example, you get a sudden glut of people looking to sell their securities - say, because all the baby boomers start dipping into their retirement savings at about the same time - that isn't matched by a sudden glut of people looking to buy those securities, then a lot of retirees are going to suddenly discover that their life savings is basically just evaporating at the very moment when they started to rely on it. Some Gen Xers and Millennials might remember having seen a small version of this play out a decade or two ago, when everyone tried cashing out of their comic book collection at about the same time.