It masquerades in part an overt denial of unpleasant realities, cover-ups, broken promises and inconsistencies. Lying as the norm in your house became part of what you knew and what could be useful to you. At times, it made life much more comfortable. If you lied about getting your work done, you could get away with being lazy for a while. It seemed to make life simpler for everybody.
Adult children judge themselves without mercy.
Your judgment of others is not nearly as harsh as your judgement of yourself, although it is hard for you to see other people's behaviour in terms of a continuum either. Black and white, good or bad, are typically the way you look at things. You know what it feels like to be bad, and how those feelings make you behave. And then if you are good there is always the risk that it won't last. So either way you set yourself up.