Just like a Ponzi scheme, S/S could survive only by bringing new workers into the program. At first, it was only private sector, non-farm workers. Then Farm workers, next some public employees were brought into it (kicking and screaming). Along the way, nearly all women joined the workforce and began to pay into the system (though there was no corresponding adjustment from the assumption that women were stay-at-home home-makers and care-givers. Now, there is not large body of people to rope into the system to keep it afloat - so it is sinking. Rapidly.