Typically, economists believe that people make decisions based on rational considerations. They believe that people make their business decisions based on a consideration of the marginal costs and benefits of that decision.
However, it does not seem to me that such an approach is sufficient. I believe that people very often take decisions based on emotion rather than on rational considerations. Businesspeople will decide things based on their fears rather than on a more objective consideration of the facts, for example.
Perhaps even more to the point, much of the current economic crisis was caused by people taking decisions based on their feeling that nothing could go wrong rather than on a level-headed analysis of the conditions.