Economists Ian Ayres and Barry Nalebuff say that people in their 20s and 30s should take out their retirement savings and buy stocks on margin. They think that people “seriously under-invest in the market for the first 25 years of their working life,” and that if young people did invest they would reduce their overall risk by 20%. “The increased market exposure when young allows you to have less exposure later on,” says Nalebuff.