It is a thoughful work that discusses self perception and the perception of others and the way that witnesses see what they think they are seeing rather than what they actually see, and the way that a leading question can lead a witness to believe they saw something that, really, they didn't. It also paraphrases Einstein's "it is the theory tht determines what we observe".
He also uses a quote from Dostoevsky's Notes from the Underground, that discusses what it means to be human.
Every man has some reminiscences which he would not tell to everyone, but only to his friends. He has others which he would not reveal even to his friends, but only to himself, and that in secret. But finally there are still others which a man is even afraid to tell himself, and every decent man has a considerable number of such things stored away. That is, one can even say that the more decent he is, the greater the number of such things in his mind.