People are rational animals, right. Before we make a choice, we calculate the cost to benefit and decide if the decision is best. Or are there irrational forces that sway us from the rational course. That is the idea behind the book Sway: The Irresistible Pull of Irrational Behavior by brothers Ori and Rom Brafman.
One of the common forces that sway us is loss aversion. People hold onto a bad stock hoping to recoup the loss and end up losing everything. Captain Van Zanten, head of the airline KLM's safety program was so concerned with the money the airline would have lost if he did not take off prior to his mandatory rest period, attempted to take off in without waiting for clearance in conditions so foggy that he could not see the other 747 on the run. The passengers in the other plane were unharmed but Van Zanten's plane did not completely clear the other plane and blew up in the air killing everyone on board.
The next swaying force is commitment. If Van Zanten had not been swayed by his loyalty to his airline and to his personal record, lives might not have been lost. Commitment can be so powerful that in an auction for a $20 bill where the second place bill still has to pay, the final price can be bid up to hundreds of dollars.
The other forces that sway us are value attribution, diagnosis bias, the chameleon effect, sense of fairness, the anticipation factor and the dissenting voice. For each of these sways the Brafman brothers give examples but each swaying factor played a part in the Van Zanten affair.
One interesting example of the diagnosis bias is a study by Dan Ariely. The study involves A SoBe drink that purports performance enhancing effects. In this study, students were given SoBe and the cost was deducted from their student accounts. 3 different groups were tested, one with regular price SoBe, one with discounted SoBe and a control group who had no SoBe. The groups were informed about the supposed performance enhancing effects. The group that drink the regular price drink performed better then then the control group. Before you go out and buy SoBe to increase your performance, guess how the cheap SoBe drinkers did. They actually performed worse then the control group.
There are more great studies listed in the book. No one study ever conclusively proves anything but they all illustrate how people are easily swayed by non-rational thinking.