Business men play a mixed game of skill and chance, the average results of which to the players are not known by those who take a hand.
 John Maynard Keynes, The General Theory of Employment, Interest and Money (1936). copy citation

Context

“though, if we exclude the exploitation of natural resources and monopolies, it is probable that the actual average results of investments, even during periods of progress and prosperity, have disappointed the hopes which prompted them. Business men play a mixed game of skill and chance, the average results of which to the players are not known by those who take a hand. If human nature felt no temptation to take a chance, no satisfaction (profit apart) in constructing a factory, a railway, a mine or a farm, there might not be much investment merely as a result of cold calculation.” source