Halo effect
The halo effect is letting one positive trait, such as good looks or charm, shape your opinion of a person's other, unrelated traits. The reverse, where one bad trait colors everything, is sometimes called the horn effect.
In everyday life
In mock-jury experiments, people tend to judge attractive defendants a little less harshly, even though looks say nothing about guilt.
Because a new coworker is funny and well dressed, you assume he must also be good with budgets and hand him the finance project without checking his experience.
Why your mind does this
Trusting people and things we know is usually safe, because familiarity means we have dealt with them before without harm. Favoring our own group helped our ancestors cooperate with the people they depended on. Liking what is close and known also saves the effort of judging everything from scratch.
How to spot it
Ask whether the trait you admire has anything to do with the quality you are judging.
How to counter it
Rate each quality you care about separately, using concrete evidence for each one.
Same family: Familiar is better
SourcesThorndike (1920)·Wikipedia