Even such trait theorists as Allport reject this notion.
Invariant behavior means psychopathology.
This is expressed in a number of hypotheses that research has evaluated. No, raters can agree on which traits apply most strongly to which person, showing discrimination across individuals. No, Although it is well known that the Barnum effect exists, raters can still discriminate on which characteristics pertain to which individuals. Data has shown that inter-rater agreement improves as observers view the target person over time. A stereotype hypothesis would say that rating would stay the same because they are based on stereotypes, not real people.