For those who invest in only index funds, what people think that they will truly continue to go up forever, albeit going down and up at times? What is there to suggest that some new financial tool will not replace index funds? There was a time before index funds after all. Is VTI and VOO truly that safe? For those with a long time horizon, will these index funds truly keep going up? If they’re 270 today, can we expect 2000 plus in 40 years?