We study experimentally when, why, and how people intervene in others' choices. Choice Architects (CAs) construct opportunity sets containing bundles of time-indexed payments for Choosers. CAs frequently prevent impatient choices despite opportunities to provide advice, believing Choosers benefit. We consider several hypotheses concerning CAs' motives. A conventional behavioral welfarist acts as a correctly informed social planner; a mistakesprojective paternalist removes options she wishes she could reject when choosing for herself; an ideals-projective paternalist seeks to align others' choices with her own aspirations. Idealsprojective paternalism provides the best explanation for interventions in the laboratory and rationalizes support for actual paternalistic policies.