{Muhammad bin Salman is one of the world’s most secure autocrats. He has no need to pay off rivals or buy elections. Yet by 2030 his government will have spent almost $3trn on Vision 2030, a plan to transform Saudi Arabia’s economy. Officials are backing man-made islands, luxury hotels and electric-vehicle factories. “They will take anything that has the smallest chance of creating economic growth, even if it is in decades,” says a megaproject executive, “even fantasies and failures.”}