"Think your friends know you pretty well? Think again," write Andrew D. Gershoff (University of Michigan) and Gita Johar (Columbia University) in the March 2006 issue of the Journal of Consumer Research. "We make our worst estimates for our closest friends. This is important because it affects how willing we are to rely on our friends' advice and word-of-mouth recommendations."
Why do we think our friends know us better than they really do? One explanation, according to Gershoff and Johar, is that it protects the relationship, at least in our minds. "To maintain our self image we want to believe that we are important to others, particularly to others we care about. So when we think about our close friends, we are more motivated to think they know us well compared to our less close friends, and so we overestimate more for our close friends."
The researchers conclude that suggestions from our closest friends about matters of taste, such as movies or restaurants, may not be as helpful as we think they are. However, they add, "there is more to friendship than getting good recommendations."
Andrew D. Gershoff and Gita Venkataramani Johar. "Do You Know Me? Consumer Calibration of Friends' Knowledge." Journal of Consumer Research. March 2006.