Thanks for the replies. Maybe it's not a simple question that boils down to one initial reason. I was thinking it is out of fear and shame too. Maybe it's core is about a person's deep need to avoid being "powerless" in some way. Maybe it is someone's need to figure out a way to create their own reality where they can give themselves more control then they experience in their reality. An effort to live a fantasy evolves and the person decides to make that happen even if they need to lie and exaggerate and manipulate.

Part of the reason I am asking this is because of how bad things got in the last years of my parent's lives. It turned out that my older sister had manipulated my parents into setting up their Will in a way that gave her all the power. She manipulated them when they were both mentally declining. I found out that my sister began taking money from them and they were not even aware she was doing so. When a judge demanded she present an accounting because both me and my brother wanted to know where all there money went, my sister listed all the withdrawls SHE and her daughter took and accused me of doing.

What I have been struggling with is not only disbelief but a lot of disappointment not only in her but myself for not seeing just how bad things were. I have expressed disbelief about how she can live with herself and how I myself could never do the things I have come to realize she chose to do. I even struggle with "how could I have loved and trusted someone that could do these things?".