People mistakenly think they can hide those parts of their personality they don't want the world to see, and reveal only the parts they are willing to let others know about.
But the truth is that even the deepest parts of a personality stand out on the tip of your nose for everyone to see - everyone except yourself.
A person thinks he knows himself, but even that he doesn't know. Similarly, a person thinks he knows how his voice sounds, but when he hears himself on a tape he sounds strange. He can't believe it's really him while others recognize his voice right away. This is also true of our drives and motivations: we deceive ourselves as to what we really think, while to an outsider it is obvious.
Rabbi Mendel Kaplan "Reb Mendel and his Wisdom" by Yisroel Greenwald