Egocentric bias is the tendency to overstress changes between the past and present in order to make ourselves look better than what we really are. According to the results from several conducted studies, individuals are also more likely to favor circumstances that are beneficial to themselves compared to those that favor to the people around them.
As a matter of fact, an egocentric bias is one of the "seven sins" of our memory and essentially reflects the prominent role played by the self when encoding and retrieving episodic memories. For instance, an egocentric bias is displayed when a fisherman "remembers" catching bigger fish than he had actually caught in reality. Here, it becomes clear that this type of bias is fundamentally a memory distortion produced by current knowledge and beliefs, and leads one to remember the past in a self-enhancing manner. 
Besides simply claiming credit for positive outcomes, which might simply be self-serving bias, people exhibiting egocentric bias also cite themselves as overly responsible for negative outcomes of group behavior as well (however this last attribute would seem to be lacking in megalomania).
This may be because people's own actions are immediately accessible to them than others' actions. This is an example of what is called the availability heuristic.
This bias suggests that people remember the past as they want it to be rather than the way it was, making themselves look good in retrospect.
Egocentric bias in estimates of consensus could be interpreted to support and/or justify one's feelings that their own behavioral choices are appropriate, normal or correct.
Motivational factors may also be a factor; one's sense of self-esteem may be enhanced by focusing on, or weighting more heavily, one's own inputs. People's own inputs and contributions tend to be more available (and more likely to be recalled) than the contributions of others. 
One study found that egocentric bias influences perceived fairness. Subjects felt that overpayment to themselves were more fair than overpayment to others; by contrast, they felt the underpayment to themselves were less fair than underpayment to others. Greenberg's studies showed that this egocentricism was eliminated when the subjects were put in a self-aware state, which was applied in his study with a mirror being placed in front of the subjects. When a person is not self-aware, they perceive that something can be fair to them but not necessarily fair to others and so fairness was something biased and in the eye of the beholder. When a person is self-aware, there is a uniform standard of fairness and there is no bias. When made self-aware, subjects rated overpayment and underpayment to both themselves and to others as equally unfair. It is believed that these results were obtained because self-awareness elevated subjects' concerns about perceived fairness in payment, thereby overriding egocentric tendencies.
Egocentric bias has influenced ethical judgements to the point where people not only believe that self-interested outcomes are preferential but are also the morally sound way to proceed.
In social context, egocentric bias influences people to choose a social circle that is capable of maintaining one's positive traits. Study shows that one's choice of friend or social circle is likely to be dependent on the amount of positive feedback received. 
A best known example of egocentric bias is a study Ross, Greene and House did in 1977. Students are asked to walk around a campus with a sandwich board that has the word "repent" on it. People who agreed to do so (50%) estimated that most of their peers would also agree to do so (average estimation 63.5%). Vice versa, those who refused to do the experiment think that most people would make the same decision as theirs.
Another study of egocentric bias took place in Japan. Subjects were asked to write down fair or unfair behaviors that they themselves or others did. When writing about fair behavior, they tended to start with the word "I" rather than "others". Likewise, they began unfair behaviors with "others" rather than "I". However, in this study there were gender differences detected; Japanese women, compared to men, remembered the behaviours of others more than their own, and were also more probable to characterize fair or unfair behavior to others compared to themselves.
Considered to be a facet of egocentric bias, the false-consensus effect contributes to people believing that their thoughts, actions, and opinions are much more common than they are in reality. They think that they are more normal and typical than others would consider them.
Results from a study comparing the perceptual distortion and motivational explanations of egocentric bias in estimates of consensus showed that an egocentric bias in estimates of consensus was more likely a result of perceptual distortion than of motivational strategies.
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- Greenberg, Jerald. Overcoming Egocentric Bias in Perceived Fairness Through Self-Awareness. American Sociological Association. Social Psychology Quarterly , Vol. 46, No. 2 (Jun., 1983), pp. 152-156. OCLC 483814059
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- Tanaka, K. (September 1993). "Egocentric bias in preceived fairness: is it observed in Japan?". Social Justice Research 6 (3): 273–285. doi:10.1007/BF01054462.
- Tanaka, K. (September 1993). "Egocentric bias in perceived fairness: is it observed in Japan?". Social Justice Research 6 (3): 273–285.