People who think they are clever believe that it's only natural that they are able to decide better than thousands or millions of people that are "not so clever".
They overestimate their cleverness and, through Halo Effect, think that they must make better, clever decisions on all subjects and situations.
People who are actually clever are clever enough to know this is not true.
Power attracts more people that think they are clever than people who actually are.
With time, that becomes clear.