Lean proved this program correct; then I found a bug

A programmer used Lean to prove the correctness of a program, but later found a bug, highlighting the limitations of formal verification methods. This incident matters because it shows that even rigorous methods can fail. To avoid similar issues, engineers should consider the complexity of their code and the limitations of their verification tools. They should also regularly test and review their code to catch potential bugs. This will help ensure the reliability and safety of their software.