The author proposes an updated theory of animal spirits that builds on Keynes’s insights and extends them by incorporating recent developments in neuroscience and psychology. He places animal spirits in a broader perspective of two systems of reasoning, each pertaining to different degrees of uncertainty. He examines how animal spirits form beliefs by way of analogical reasoning, the mental shortcuts they use, and the role of emotions. He outlines how confidence is biased and distorts business forecasts. The brain seems to seek to achieve the highest level of confidence, and maintains this level by distorting subsequent cognitions so that they substantiate the initial view. Animal spirits are ambivalent. Emotions signal whether we under- or overachieve. Animal spirits push us to take greater or fewer risks in order to reach and secure our objectives. At the same time, they provide incentives to update or change our beliefs and goals, so that they may be more sensible. However, animal spirits also conclude hastily and seek confirmation of their beliefs; they elaborate patterns out of nothing and rely on stereotypes; and emotions may distort judgment. Interestingly, so long as confidence remains high, animal spirits continue to rule the roost; when confidence plummets, logic and calculation enter the fray.