In life, we often wear masks. As a speaker I heard this weekend said, there's Who we are, Who we THINK we are, Who we pretend to be, and Who others think we are.
In novels, this is also true for the characters we create. And often it is the differences in those 4 images that generates plot. If you're a writer and you're stuck planning out a story, a useful exercise might be to write down for each major character the answer to those four categories.
By the same token, in real life, it can be useful to look at those four categories about ourselves. Looking at the discrepancies might give us insight into what might be causing problems and how maybe, just maybe, we can address the issues and resolve some of them. It's not for the faint of heart, of course, but the results can be very powerful.