In the past, men could design a multi-generational plan with certain safe assumptions: the dollar would be a stable currency, the US Economy would always be among the top industrialized economies in the world, easy access to goods and services would be a constant.
Not to sound apocalyptic, but those assumptions are no longer reliable.
As this recent Wall Street Journal article points out, the reign of the Dollar is near an end. I am not going to delve into this now, but the only thing that has kept the US Economy afloat has been the fact that the Dollar is the official global reserve currency. When that goes away, things get very bleak very quickly.