Stereotypes are beliefs that associate groups of people with certain traits. This association may be thought of as a probability judgment. As such stereotypes are very difficult to disconfirm. For example, you may have the belief that English people are usually reserved. Because there is great variability among people in any group, stereotypes are bound to be incorrect much of the time.
People believe that stereotypical sex differences are much greater than they are in reality.
Hypothetical distribution of a characteristic by sex. These small differences cannot account for the large observed differences in gender roles, occupational roles, etc. Spatial ability can't account for it. The spatial differences are so small that you'd expect very close to a 50-50 distribution of male to female engineers. A very muscular man may cue a male sex role stereotype.