Children start out as essentially guileless. They cry, but, when very young, have limited ways to express their needs. As they become a little older, deception first starts.
Deception is based on fear: fear of pain, rejection, or of not gaining something desired. Deceiving is a habit acquired early, and it becomes a way of life for some. I think none of us truly want to know everything about anybody. We've all made mistakes, or less than optimal decisions, and it's rare to find anyone who hasn't done at least a few things that are deeply regretted.
A few people have swung to the opposite pole: they brag about their mistakes and indiscretions, as though daring the reader or listener to judge them. In either case, an emotional connection to any issue discussed still exists, whether it's concealment or exhibitionism. How rare and refreshing, then is a quiet "You can ask me anything."