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I guess that every data manager on earth has suffered that awful moment when you realize you shouldn't have pressed return on the command you just entered and that you've lost some large amount of work that will take a day or so to recover? Particularly if you're used to an OS like windows that doesn't REALLY delete stuff until you clear out the recycle bin, and suddenly remember you're in the less forgiving environment of Unix or VMS! It's even worse when you're using some GIS data formats where the basic unit of data is the contents of a directory, and messing with any part of those contents can irretrievably (well, almost) damage the entire dataset (yes, old and hoary users like me do know ways to reconstruct the data, but it isn't for the beginner and is error prone!). Or an SQL "Delete" command with autocommit on and an untested "where" clause that doesn't do what you thought it did...