Margin of Safety Core rule: commit a buffered number when residual uncertainty plus breach cost can cause ruin or costly failure. Margin covers estimation error; it is not free slack for laziness. When to Use - Capacity, timeouts, pool sizes, queue depths, storage, or SLA numbers under load uncertainty - Timeline or budget commitments where underestimation is costly - Architecture headroom when scaling or recovery is slow - Any public or production commitment where being wrong has asymmetric downside When NOT to Use - Breach is detected immediately and fixed near-zero cost (fast auto-scale, l…