Self-serving bias is a heuristic of attribution used to maintain and increase one’s self esteem. This occurs for both negative and positive events. For positive events, we are likely to attribute it to choices we make or personal traits. Conversely, for negative events, we attribute the outcome to situational factors, or other factors outside of our control. This behavior is common and fairly universal. One exception is for depressed individuals, who are more likely to attribute negative outcomes to their own faults. One cause of this bias is optimism; negative outcomes tend to surprise people, so they are likely to produce situational rather than personal reasons for this negative event. Self-serving bias can be detrimental in that it can make people less likely to learn from their mistakes, as well as more likely to believe that their success is their fault, rather than largely due to luck.
A classic example of self-serving bias pertains to a student receiving a grade on an exam. When he gets an ‘A’, he believes that he got this grade due to his hard work and intelligence. When he gets a ‘C’, it is because the teacher didn’t teach well, or the material was too difficult, or another similar reason.