Illusion...

People tend to believe that their thoughts and feelings are more apparent to others than is actually the case, a belief researchers call the illusion of transparency.
In one study, participants played a variation of the “two truths and a lie” game.

Thinking that others could see right through them, the participants overestimated the extent to which others could detect their lies. 

Another group of participants was asked to conceal their feelings after drinking either Kool-Aid or a nasty, vinegar-based drink. 

Though participants believed they were not very good at hiding their reactions, observers could not tell which drink they had consumed.