From Insight :

...other people generally see us more objectively than we see ourselves. Psychologist Timothy Smith and his colleagues powerfully demonstrated this in a study with 300 married couples in which both partners were being tested for heart disease. They asked each participant to rate both their own and their partner's levels of anger, hostility, and argumentativeness- all strong predictors of the illness- and found that people's self-ratings were infinitely less accurate than those of their spouses. Another study asked more than 150 Navy officers and their subordinates to rate the officers' leadership style, and found that only the subordinates could accurately assess their bosses' performance and promotability.