If the economy is to grow, someone has to set aside resources today and, instead of consuming them, use them to try to increase future production. Anyone could do that, but, empirically, most people don’t want to do it, or don’t want to do very much of it. Most people, if they acquire some extra money, will shortly spend it.So it falls to a small group of people to do most of the investing. In return for forgoing immediate consumption, they get a little bit more expected money at a future date.