As I'm reading The Gathering Storm, I can not help but notice occasions of psychological biases that hindered important decision-making, much to the detriment of Europe and the world. The main one (and easiest one) I've noticed is confirmation bias. Below are two examples I thought particularly illustrating.
Churchill made some comments on Hitler's violation of the Munich Pact, on the belief that the British Intelligence Service had collected good intelligence but it was somehow neglected by the government:
How was it that on the eve of the Bohemian outrage [the splitting up of Czechkoslovakia after the Munich Pact] Ministers were indulging in what was called "sunshine talk" and predicting "the dawn of a Golden Age"? How was it that last week's holiday routine was observed at a time when clearly something of a quite exceptional character, the consequences of which could not be measured, was imminent?... It seems to me that Ministers run the most tremendous risks if they allow the information collected by the Intelligence Department, and sent to them, I am sure, in good time, to be sifted and coloured and reduced in consequence and importance, and if they ever get themselves into a mood of attaching weight only to those pieces of information which accord with their earnest and honourable desire that the peace of the world should remain unbroken. [Emphasis mine] (Location 5987 to 6000, Kindle Edition)
And Mr. Duff Cooper, First Lord of the Admiralty who resigned after the Munich Pact (where Britain and France decided allow Hitler Czechoslovakia rather than honor France's guarantee of Czechoslovakia's defense against invasion), from his resignation speech given in the House of Commons (incidentally for 40 minutes and without needing to refer to any notes):
The Prime Minister [Neville Chamberlain, of the Conservative Party, which is curious, because today would you ever expect a Conservative in Britain or America to be in favour of appeasement over the mailed fist?] has confidence in the goodwill and in the word of Herr Hitler, although when Herr Hitler broke the Treaty of Versailles, he undertook to keep the Treaty of Locarno, and when he broke the Treaty of Locarno he undertook not to interfere further, or to have further territorial claims in Europe. When he entered Austria by force, he authorised his henchmen to give an authoritative assurance that he would not interfere with Czechoslovakia. That was less than six months ago. Still the Prime Minister believes he can rely upon the good faith of Hitler. (Location 5518-5544, Kindle Edition)
This also seems to be confirmation bias, because Chamberlain felt he could trust Hitler (eerily similar to Bush's words about trusting Putin by looking into his eyes) and hence ignored the abundance of evidence to the contrary. That's a key point of confirmation bias, only using evidence that supports your thesis. Though I have to wonder what evidence Chamberlain had for his viewpoint in the first place, given that a good number of Hitler's transgressions occurred during the prior Prime Minister's (Baldwin) tenure.
A further comment: confirmation bias is the bane of any thinking person. Regardless of the field where intelligence needs to be applied, be it medicine, science, economics, banking, scholarly research, etc, one of the worst dangers is to only read articles, opinions, and research that accords with your worldview. To not know the Opposition's viewpoint is to avoid subjecting your thoughts to arguments that may illustrate weaknesses in your thoughts which may need to be rethought and may have some wrong points only discovered by looking at the other side's arguments. Or you may have avoided addressing certain subjects that need to be addressed, even though your argument may overall be correct. Regardless, I would argue that confirmation bias is a terrible risk, one worth addressing.
Sometimes the consequences of not addressing potential bias are minimal. But other times, like 1938, the consequences were terrible.