Such as our recent history can demonstrate

“The greater our prosperity, moreover, the more should we seek the counsel of friends, and the greater the heed that should be given to their advice. Under such circumstances also we must beware of lending an ear to sycophants or allowing them to impose upon us with their flattery. For it is easy in this way to deceive ourselves, since we thus come to think ourselves duly entitled to praise; and to this frame of mind a thousand delusions may be traced, when men are puffed up with conceit and expose themselves to ignominy and ridicule by committing the most egregious blunders.” – Marcus Tullius Cicero, De Officiis (trans. Miller)