The Economist studies the phenomenon:
The existence of the so-called halo effect has long been recognised. It is the phenomenon whereby we assume that because people are good at doing A they will be good at doing B, C and D (or the reversebecause they are bad at doing A they will be bad at doing B, C and D). The phrase was first coined by Edward Thorndike, a psychologist who used it in a study published in 1920 to describe the way that commanding officers rated their soldiers. He found that officers usually judged their men as being either good right across the board or bad. There was little mixing of traits; few people were said to be good in one respect but bad in another.
Later work on the halo effect suggested that it was highly influenced by first impressions. If we see a person first in a good light, it is difficult subsequently to darken that light. The old adage that “first impressions count” seems to be true. This is used by advertisers who pay heroic actors and beautiful actresses to promote products about which they have absolutely no expertise. We think positively about the actor because he played a hero, or the actress because she was made up to look incredibly beautiful, and assume that they therefore have deep knowledge about car engines or anti-wrinkle cream.