Some people may see, hear or sense things that clearly are not there. They may also have beliefs that they cannot change even with solid evidence to the contrary. They may find it difficult to express their thoughts. They may not have insight into their own state of mind.
Have a look at the quote below. Notice how real the voices seem to the person experiencing them.
Just then, surprisingly, there were voices bouncing off the wall, they were in different language that Ajax couldn't understand. "Go away!" Ajax thought, but they didn't go away, they just got louder and weirder, Ajax clamped his hands tightly over his ears as the voices magnified and his eyes were also clamped shut, and his brain was bleeding with voices that wouldn't go away. It was like being in a room of chaos!