Reversibility is the most critical quality in software decision-making—more important than predicting whether something will work. Wrong decisions are acceptable if reversible; irreversible decisions made on hope alone build systems on prayer. Reversibility differs fundamentally from iteration: iteration improves incomplete solutions incrementally, while reversibility means being able to return to the prior state before implementing a system. Confusing these two concepts leads to endless struggles and persistent doubts about whether different approaches would have worked better. The key insight: optimize for decision reversibility rather than decision correctness, as reversible mistakes are manageable while irreversible ones are catastrophic.