Brian Thomas killed his wife during a sleep terror episode. His brain, while asleep, interpreted a sound as an intruder and he acted to protect his wife, killing her instead. When he woke, he was devastated. A court acquitted him, ruling that the act was unconscious and automatic: he had no awareness and no choice. Duhigg uses this extreme case to ask the question that the whole book builds toward: if habits run automatically, below the level of conscious decision-making, when exactly are we responsible for what we do? His answer: the moment of responsibility is not when the habit runs. It is the moment you become aware that a habit exists. Once you know a habit is there, you have a responsibility to examine it. This reframes how to think about change. You are not responsible for the automatic behaviour you were not aware of. But you are fully responsible for what you do after you recognise it. Awareness converts an automatic behaviour back into a choice. And choice creates the obligation to act.