I once heard of someone who had lost a whole year's work - poetry, short stories, essays - everything.  It had been in exercise books and notepads left in a rucksack in a car parked outside the writer's new house when he was moving in.  Thieves broke into the car and stole the rucksack.  The writing was of no value to them, and would no doubt have been dumped, but he never found it.  
    I can't imagine how awful such a loss would be.  Rewriting everything exactly as it had been would be impossible, that's why I always keep copies of everything.  Not only that, but I keep a record of what files work's in, where I've sent it and the result on index cards.  It should be foolproof, yet yesterday I wasted a sunny afternoon searching for an article that was published years ago when I still used a typewriter.  I hadn't bothered to put the article on my computer, when I got one, as I had a copy of the magazine it appeared in, so it seemed like unnecessary work.  I thought I kept all the magazines with my work in them together, but of course, this one has vanished, and where is the carbon copy that should be in the file?  
    It isn't the end of the world, but it is irritating, so my advice is not only to keep a hard copy of your work and back up computer files on a cd, a memory stick, or better still, both.  Then those sneaky cousins of the tooth fairy, who steal keys, spectacles, earrings and anything else that you had in your hand a minute ago, won't be able to spoil your day.