Soft Feedback Is Kind to You and Expensive to Them
You saw the problem ten minutes into the design review and said 'solid start, think about the failure cases.' They heard approval and built for three weeks on a design you knew was cracked. Softening the verdict spared you one bad minute. They paid for it in weeks, in a public correction, and in praise from you they can no longer trust. You kept the comfort and they got the bill.