Why do 900 million people confide in ChatGPT despite knowing it can't reciprocate? Charles Duhigg, Pulitzer Prize–winning author of Supercommunicators, reveals that AI conversations feel safe but lack the vulnerability and judgment-withholding that create genuine human connection—making them sophisticated diaries, not true relationships. Humans unconsciously synchronize heart rate, breathing, and neural activity during genuine conversations, a process called neural entrainment that creates the dopamine release we associate with feeling connected.