Capitalists can make money in their sleep, but they can lose it, too, especially recently.
Capital is savings. That is how one becomes a capitalist: they save. Once you have savings, you can risk those savings on investments. In other words, capitalists are rewarded in their sleep, because they are always bearing the risk of what others are doing with their resources.
Capitalists are indispensible to a well-functioning and growing economy, since savings represent the pool of resources with which to invest and increase future output. With capitalists, that is, people who save by foregoing consumption, and then risk those savings by investing in others, more people than before can have the opportunity to succeed in life. For example, many people on this forum could never have attended college, if it were not for capitalists taking a risk by allowing others to use their savings.