[mtberatwork]

Compounding interest...if you start early enough and take advantage of employer contribution matching, etc. But most people in the US won't retire as millionaires, let alone even retire. Unforeseen life events often cause people to dip into retirement savings and in some cases wipe out any gains. Also, once in retirement, life in the US can still be quite expensive. For example, Medicare and all the additional supplemental insurance(s) you need is absurdly expensive for retirees. Everything in the US is "out of pocket".