Can you know someone better than they know themselves?

There have been times when I thought I had a true insight into someone else that they didn’t get. Their behavior was a mystery to them, but not to me. If I told them what I thought, they usually disagreed with it and did not take it well. Did I know them better? I don’t know.

Yesterday I had a conversation that similar to many that people with bipolar disorder have. Someone asks them if they are manic. They say, “No.” The person refuses to believe them. “Yes you are. You should go see the shrink or the therapist or check yourself into the hospital.”

I guess people think that because we have mental illness, we often can not see ourselves with any objectivity. Aside from the fact that no one can see themselves objectively, what do you think? Are there people who have so little insight on themselves that they don’t know what is going on? Can you know someone better than they know themselves?