Owen and Davidson studied the behavior and medical records of dozens of American and British political leaders, from Prime Minister Herbert Asquith, who took office in 1908, to President George W. Bush, who left office in 2009. Across that century, they identified a tendency among some otherwise high-achieving individuals to close themselves off from critics and to overestimate their odds of success. Neville Chamberlain wrongly believed that he could appease Hitler; Tony Blair supported the invasion of Iraq even after his envoy informed him that the plan had “no leadership, no strategy, no coördination,” among other defects. When a leader succumbs to hubris syndrome, the authors wrote, his experience at the top has distorted his personality and decision-making.
Here is the link to an interesting article on political hubris by Evan Osnos.