Not quite; you're probably thinking of: https://google.github.io/building-secure-and-reliable-system...
Classic.
In my first job I worked on ATM software, and we had a big basement room full of ATMs for test purposes. The part the money is stored in is a modified safe, usually with a traditional dial lock. On the inside of one of them I saw the instructions on how to change the combination. The final instruction was: "Write down the combination and store it safely", then printed in bold: "Not inside the safe!"
awesome !