i'd written a script to deploy the latest changes to the live environment. worked great. except one day i'd entered a typo and it was now deploying the same files to the remote directory, over and again.
it did that for 2 whole years with around 7 code releases. not a single person realised the production system was running the same code after each release with no change in functionality. all the customer cared about was 'was the site up?'
not a single person realised. not the developers. not the support staff. not me. not the testers. not the customer. just made you think... wtf had we been doing for 2 years???