It is preferred to believe that the intellect, statistical analysis, cognitive evaluation, abstract reasoning, and similar cognitive processes rule the decision making process. However, research in neuroscience suggests that emotion, personal bias, affective desires, and pet peevees play an equal, if not larger role, in the ultimate decision made--even if there has been significant intellectual input.
A few articles to illustrate:
Emotional Decisions: The Neuroscience of Decision Making.
The Role of Emotion in Decision Making: A Cognitive Neuroscience Perspective -- Abstract
Emotion and Reason in Decision Making.
Mind/Body, Emotions and Decision-Making