Assuming, for the sake of argument, that this guy is right about the impending financial doom, isn’t paper currency the last thing you would want your entire worth invested in?
Well, it would depend on what he really has in mind. If there were straight Deflation, then paper currency would be a lovely thing, because it would buy more and more stuff with each passing day.
What worries people is that policymakers would inevitably respond to Deflation, by spending unbelievable amounts of fiat money, precisely in order to try to create some inflationary impulse. When there’s deflation, the tendency to save becomes irresistable (because the dollars in the mattress generates high returns not in interest, but in purchasing power) which leads to further stagnation, a vicious cycle.
What that can result in is something called a Liquidity trap, where your cash earns no interest, but anything you invest it in that’s linked to the economy declines in value. So you have little risk taking, little spending because of fear of the uncertainty in the future, and ongoing stagnation in activity. Japan went into a Liquidity Trap more than a decade ago, and only the Chinese economic boom helped them to get a little bit better (but far from cured).