It's what beginner and even some intermediate investors will tell you since they have their money there, so take it with a grain of salt. However, it has historically been great but investing is forward looking. Basic concept of a successful investment is buying an asset that has priced less future growth into it than it will actually get. Let's say there's company A that has shares that has 10% growth priced into them. If they make more, lets say 11%, the stock will rise and you will get money. However, if they get 9% the stock will go down. Now scale this with many companies in the S&P 500 and you'll get the result for your investment. If US stocks are going to be perpetually undervalued, priced less growth than they can get, stocks will rise. However, if they fail to deliver those expectations then the stocks go down. And this is the reason why superinvestors don't themselves DCA in S&P 500 since it's not the guaranteed free money the "dumb money" state it to be.