Civil engineering decisions are rarely made under conditions of certainty. Whether selecting a foundation system, sizing a drainage network, or planning long-term flood protection, engineers must commit to designs while key inputs remain imperfectly known. Material costs fluctuate, regulatory frameworks evolve, hydrologic regimes shift, and societal expectations change. Traditional deterministic design, where single “best estimate” values are inserted into equations, often conceals the fragility of decisions. A solution that appears optimal under assumed parameters may perform poorly when those assumptions deviate from reality.