There is a difference between believing and knowing. You can be told or read about a story your entire life and you will believe it to be true. But when you see it for yourself you stop believing or disbelieving, because you know. Once you know, you start asking yourself a lot of questions. If a person is unable to handle the ramifications of the answers to those questions, their mind can break. If the knowledge doesn't break their mind, that person becomes completely immune to the lies. Take it from someone who knows.