So if you are a very shy and reserved person who reveals next to nothing about your thoughts and feelings to the people around you, then they will know very little about you—aside from the fact that you are shy and reserved, obviously. The danger there is that people will generally fill in the blanks themselves, imagining a whole personality

we tend to slot other people into stereotypes. I might assume that my taxi driver’s conversation won’t extend beyond the weather and the football; if I exercise my curiosity a little more I might find out about his PhD in sociology.