If you drive, you may have had the unfortunate experience of moving into the right lane, only to hit a car that was in your blind spot.  You may have taken someone out to dinner, on a date, and halfway through the meal your date says, “Excuse me, but you have something on your chin.”  You could not see it.  Sometimes people close to us will see things in our lives (attitudes, behavioral patterns) that we do not see.  We have blind spots.