Someone asked me once what I thought was one of the most basic psychological mistakes people make? After some contemplation I came to the conclusion that the "halo effect" was something I observed in others quite often. The halo effect, coming from studies in social psychology, is when an impression one has about someone (either positive or negative impressions) is generalized to their entire personality. For example, to assume that an attractive person is honest, hardworking, mentally healthy, and dependable; or, that someone seen as unattractive is more than likely lazy, dishonest, mentally unhealthy, and likely to exploit others.
Difficulties can occur when one assumes various qualities about someone based simply upon initial observations. Also, those that understand the power of the halo effect can use it to their advantage and will therefore be very careful about how they come across to those they seek something from (such as money, opportunity, votes, etc.).
Being careful not to make quick judgements or decisions, allowing for time to pass to observe consistency, or really checking out formal or informal references, are bits of advice that have some valuable wisdom running through them. What about you? Can you think of a time when you incorrectly assumed someone was one way or another, based on some impression they made upon you? Are you becoming more effective at not committing the halo effect?