The projection defense mechanism is a psychological theory which says that people deny the existence of their own negative traits and habits. Instead, they tend to blame the effects of such traits on others.
Projection also allows humans to ignore negative traits in others and assume that they are mostly like themselves. The concept of projection was first conceived by Sigmund Freud, who stated that projection is a result of having feelings that the psyche cannot deal with, so the feelings are pushed off onto someone else. Negative consequences of undesirable thoughts or traits are easier to deal with on an emotional level if they are seen as belonging to someone else.