When I was at AWS, they famously required an extensive "CoE", correction of errors, or post-mortem, in an instance of over-charging a customer $0.26.

The idea is that if we can make small billing mistakes like that, we can make large billing mistakes, and need to invest in the correctness of the systems powering billing.

I have great respect for the engineering culture within AWS during those times. I am glad to have left before seeing it degrade and decline.