Echoing what others have said, the extent to which we know ourselves depends in (large?) part to the range of life experiences we've endured. Extremes might be

Echoing what others have said, the extent to which we know ourselves depends in (large?) part to the range of life experiences we've endured. Extremes might be enjoyment such as roller coaster or paintball wars, grief from losing a loved one, pride in seeing your child excel at a sport, fear while being under fire in a war zone, pain in a boxing ring,... If you haven't had extreme experiences, can you really be certain how you'd react and how intense those reactions would be? Can you really place your day-to-day experiences in context of the entire range of possibilities? I've found that, in general, people with less life experience tend to under-react to some circumstances and overreact to others, for example. The other half would be how honest we are with ourselves on reflection of those experiences. (Did I really enjoy it that much? Was it really as painful as I felt at the time? Why did that circumstance cause so much embarrassment? I believe others would not have felt it so poignantly...) It's a complex endeavor, but certainly worthwhile, especially if you're in or aspiring to be in, leadership. Leaders who don't know themselves are less likely to supplement their weaknesses and also less likely to exploit their strengths.