The halo effect shows how your impression of a person will influence your overall view of a character. This is most obvious when a person is physically attractive. It’s been known for a long time and proven in multiple studies that we rate intelligence and positive qualities of a person who we find attractive as higher than a person whom we are not attracted to.
This is based on the warped assumption that attractive equals good and ugly equal bad. Why do you think you never really see beautiful monsters or demons, but angels always seem to look like models?
The halo effect can be seen regularly with teachers. When their favourite students make a mistake on an exam, they might just assume that the student just had a bad day and not let it affect the rest of the questions as they assume the student knows the answer and just made a small mistake. However if a troublesome student makes the same mistake, they will tend to treat that students paper more harshly when grading. Exam papers and coursework in UK universities are often marked by 2 separate people to protect from this kind of bias.
However, this principle does work both ways and if we don’t see a person as attractive, we’re far more likely to perceive them as having negative qualities, even if their behaviour and actions are identical to those of the attractive person. This is termed the horns effect.
I like to describe the halo/horns effect as a filter. If you attach a blue filter to sunglasses, all objects, no matter what colour, appear blue.
So, if you form the opinion that a person is lazy, then everything they do will be passed through a “lazy” filter and just reinforce your belief.
While under the influence of the halo or horns effect, we are also far more likely to fall into the trap of correspondence bias.