Trait ascription bias is the tendency for people to view themselves as relatively variable in terms of personality, behavior and mood while viewing others as much more predictable in their personal traits across different situations. This may be because our own internal states are much more observable and available

Availability heuristic

The availability heuristic is a phenomenon in which people predict the frequency of an event, or a proportion within a population, based on how easily an example can be brought to mind....

 to us than those of others.

This attributional bias

Attributional bias

In psychology, an attributional bias is a cognitive bias that affects the way we determine who or what was responsible for an event or action...

 has an obvious role in the formation and maintenance of stereotype

Stereotype

A stereotype is a popular belief about specific social groups or types of individuals. The concepts of "stereotype" and "prejudice" are often confused with many other different meanings...

s and prejudice

Prejudice

Prejudice is making a judgment or assumption about someone or something before having enough knowledge to be able to do so with guaranteed accuracy, or "judging a book by its cover"...

, combined with the negativity effect

Negativity effect

In psychology, the negativity effect is the tendency of people, when evaluating the causes of the behaviors of a person they dislike, to attribute their positive behaviors to the environment and their negative behaviors to the person's inherent nature...

.

A similar bias on the group level is called the outgroup homogeneity bias

Outgroup homogeneity bias

The outgroup homogeneity effect is one's perception of out-group members as more similar to one another than are in-group members. I.e. "they are alike; we are diverse". The outgroup homogeneity effect, or "relative outgroup homogeniety" has been explicitly contrasted with the "outgroup...

.