Emotion is essential to human survival

http://www.economist.com/surveys/displaystory.cfm?story_id=E1_RQDSNSS

It is widely assumed that emotion and rationality are somehow opposed to each other, and that rational decisions are better than emotional ones. In fact, emotion and reason work closely together

although he could summarise the choices available in a given situation as well as anyone else, without his emotions to guide him he could not actually make a choice

合理的な思考と感情が結びついて、初めて意思決定ができる。要するに、意思決定は突き詰めて言えば価値判断であり、価値（好き嫌い、善悪など）と感情とは切り離せない関係にあるということじゃないかと思う。
平たく言えば、たとえば今日は家で食事するか外で食事するかの決定は、合理的思考だけでは決めることができない、ということかな。