Children experience everyday stimuli as highly emotional, novel, and memorable, whereas the same stimuli often lose their impact in adulthood. In this paper, we propose a unified mathematical framework describing this phenomenon as a dimensional collapse of stimulus eval- uation. We introduce a stimulus intensity λ raised to a perceptual exponent n, representing the effective dimensionality of evaluation. We demonstrate that habituation, tolerance, and repetition-seeking behavior naturally emerge as n decreases toward unity. This framework uni- fies childhood sensitivity, artistic habituation, addiction, and cultural maturation within a single evaluative model.