We examine the role of institutional trust in shaping compliance with legal rules, focusing on the alignment between a law’s design and its enforcement. Citizens determine their behavior based on institutional trust in the legal system and the expected penalty for violations, conditional on the government’s enforcement efforts. Discrepancies between declared laws (de jure) and their implementation (de facto) erode trust, reducing voluntary compliance. By modeling the reciprocal relationship between citizens and governments, we show that even well-intentioned laws require fairness and consistency to build trust and achieve their objectives through effective and predictable enforcement.