In the book 'Fateful Choices' by Ian Kershaw, there is a chapter on Japan's decision to attack the USA, and what was interesting in the book, was the fact that the majority of the decision makers in the Japanese cabinet were well aware how high risk the attack would be, and that they realised that the total defeat of Japan was highly possible, if not probable. The problem for the Japanese was the fact that if they didn't launch this attack ( and the sooner the better) the oil embargo, imposed by both the USA and Britain on Japan for her military actions in China, would cause the total collapse of both their economy, and their fighting capability in China, and if they caved in to the demands of the US, this would in their eyes, also led to the eventual loss of their empire in China, and a complete loss of 'face' by the government in the eyes of the Japanese public. Rather than face this loss of 'face', the military led government of Japan was prepared to go to war, against an enemy who was far stronger than them in the hope that somehow Japanese 'fighting spirit' might overcome the vastly greater economic muscle of the USA and Britain.