Have you yet had a moment when something you knew from personal experience, a long-known concrete memory of your own, turned out to not be true? Have you experienced when an event you clearly remembered proved not to have happened?
When you identify with what you think you know, then it shakes you up to discover that what you knew could never have been true. If you are what you know, then when what you know is wrong, what are you then?
When you identify yourself with what you think you know, then you live in false existence.
Practice Not-Knowing.
Matthew Roy Osborn 