Every night spent in an unfamiliar place is, in some quiet way, a negotiation between the ancient brain and the modern world. Sleep researchers have confirmed what travelers have long sensed: the mind does not simply surrender to rest in new surroundings, but holds a portion of itself in reserve — a relic of evolutionary vigilance that once meant survival. This phenomenon, known as the first-night effect, costs most people twenty to thirty minutes of their deepest sleep, and it touches nearly everyone, from the frequent business traveler to the occasional hotel guest. Understanding it, researc