Only one-third of American adults have an IRA, and just 18% actively contribute to their account to save for retirement, according to a 2016 survey by financial-services organization TIAA. That means than one in five people take advantage of the massive wealth-building and tax-saving potential of IRA investing. Let’s go over why so many Americans are passing on IRAs — and why almost none of their reasons are good enough to decline such powerful retirement-saving tool.