🔗 The code review that cost $2 million

Why engineering's favourite quality ritual fails to catch the bugs that matter

The pull request had 47 comments. Three senior engineers spent a combined 4.2 hours reviewing it. They flagged a misleading variable name, suggested extracting a helper function, and questioned whether the documentation matched the implementation. The code was approved on Thursday afternoon. By Friday evening, the company had lost $2.1 million.

The bug was visible in the diff: a validation function expected 21 input fields but received only 20. Under normal conditions, the mismatch caused no problems. Under production load on a Friday afternoon, it triggered a cascade of failures that took down the payment processing system for three hours. The post-mortem identified the root cause in minutes. The fix took four lines of code.

This pattern recurs with depressing regularity. Code review, the industry's primary quality gate, consistently fails to catch the bugs that matter most. The ritual continues because it feels rigorous. Engineers believe it works. The economics tell a different story.