For the most part, we rely on market outcomes.
People save and invest freely, take risks and earn returns based on that risk.
We instituted Social Security not out of doubts about the value of this financial system, but from a recognition that many people save too little and find themselves impoverished at retirement, disability, or after the death of a bread winner. We established Social Security, in short, to assure and adequate basic income that can form the foundation for additional work-related pensions and private saving. But we wanted to make absolutely sure that people who had worked steadily did not have to go on the dole to receive a basic income. A privatized system cannot achieve this objective reliably. The reason is that asset values, interest rates, and inflation all fluctuate.