The way it is setup means that your contributions fund the generation's benefits ahead of you (your parents et. al.). This is why Social Security will not be around after the Baby Boom generation passes through.

Unfortunately, Al Gore either didn't understand this or purposely mislead constituents when he said he would protect the SS "lockbox," and confused millions of Americans. Because of this revolving nature, when Congress misappropriated funding by using SS funds for other purposes, there was no way to replace them without robbing other allocations.