"The system is not intended as a substitute for private savings, pension plans, and insurance protection. It is, rather, intended as the foundation upon which these other forms of protection can be soundly built. Thus, the individual's own work, his planning and his thrift will bring him a higher standard of living upon his retirement, or his family a higher standard of living in the event of his death, than would otherwise be the case. Hence the system both encourages thrift and self-reliance, and helps to prevent destitution in our national life."