I always find it fun to read through these kinds of stories, particularly when we all know we've been there, are going to be there at some point, or are sitting there right now. For instance, myself and two other co-workers were working on a project several years back that involved passing around an array of values. I was building out a Swing based UI layer and infrastructure to wrap their logic and database access layer. At some point, something broke in the backend and I tracked the issue down to a block of code that was taking an array of values and constraining it to have no duplicates. The problem being that our dataset could easily have and should have duplicates. I fixed the issue with the comment "This imposed set semantics on something that is not a set."

Granted, I could have written the comment a little better, i.e. more context as to why set semantics were an issue. My co-workers later told me they found my change and spent 3 hours or so trying to figure out if I was right or not, eventually concluding I was. Of course, I was just down the hall and neither I or them thought to go ask the other about why things had changed or if it was a valid change in the first place. A little communication could saved a large amount of time ... Ah well, live and learn.