By far, user error is the single greatest threat to the security of any computer system. In Windows, files moved to the recycle bin can be retrieved until the bin is cleaned out. Recovering deleted files from your hard drive is chancy and expensive, and requires that you relinquish your computer to a technician for an unspecified length of time. When data is deleted from an NT server, it's gone. Once you clean your e-mail folders of deleted messages, they're gone.
Some user error is unavoidable.
Computing accidents are always going to be causing some poor individuals stress attacks and sending technicians on data-recovery missions. Those accidents that are due to user ignorance can be remedied by caution and education. Your best insurance against lost data is a private, current backup. For a second line of defense, you should not delete any files unless you are paying strict attention to what you're doing.