What is the halo effect?

One positive trait you notice in a person bleeds over into your judgement of their other, unrelated traits.

The mechanism is that forming a separate opinion on every quality is effortful, so the brain generalises from a single salient impression to a global "this person is good/bad" rating. Attractiveness, confidence or a warm voice can radiate outward into assumptions about intelligence, honesty or competence that you have no actual evidence for.

Example: A well-dressed, articulate candidate is rated as more competent and trustworthy in a job interview than an equally qualified but plainer candidate — the polished surface created a "halo" the interviewer mistook for substance.

Tip: When you find yourself liking everything about someone after one good impression, separate the trait you actually observed from the traits you're merely assuming.