Decades ago I worked as a leader of a small team of sysadmins. We worked around the clock maintaining server room and critical applications for an average size bank.
One of our responsibilities was to execute nightly checklists to run various processes, do backups at correct times, etc. These processes would be things like running calculations on loans, verifying results, etc.
We had a huge ream of checklists to accomplish this and we were supposed to follow them religiously.
We had two very similar applications, one our core and another a core from another bank we bought with the same application but older version and slightly different config. Consequently, we had two tracks of checklists with very similar steps.
One of those steps was to change the accounting date in the system. The application was a terminal app. We would telnet to the server, log in, then we would execute commands in the menu driven app. To change the date we would have to go to a special menu for super dangerous applications. It required the user to log in again.
Our core system, required logging in, selecting that we want to advance accounting date by one day, entering admin password again, pressing enter, then waiting for about 4 hours while the process ran. Then the process would exit back to the menu where the highlighted option would be to advance the day.
Our legacy system required logging in, selecting the option to advance accounting date, entering admin password, pressing enter, then waiting for two hours after which a popup showed to ask a stupid question where we would just always press enter, then wait for another hour until it exits to the menu.
We quickly figured out, that we can just press the enter key twice on our legacy system. The second enter press would just leave there in keyboard buffer and dismiss the popup. This was very useful for us, as this was the only operation that interrupted what would be the only time during night where we could have a kebab...
One night I made a mistake, and I pressed the enter twice... on the wrong system. When I figured out that I did it I realised the process would exit to the menu and then should ask for the admin password.
But, unfortunately, the application had a bug (or a feature). Once it exited to the menu, it came back in but for some reason it remembered that the admin password has already been entered and started advancing the accounting date again without asking for the password.
Unfortunately, the date was December 24. For entire December 24, the entire bank was unable to process any operations while we were restoring from last good backup (before day close) and then redoing eod operations. Then on December 25 as a penalty, I had to sit for entire day with accounting department observing how they manually entered all of the operations that would normally happen automatically on Dec 24th.
One extra key pressed.