What determines hard drive life? Mostly luck!

You've been advised over and over to back up your data because the issue isn't if your hard drive will fail.  It is when your hard drive will fail.  A post by Robin Harris to his blog on ZDNet summarizes recent hard drive lifespan research by Google and Carnegie Mellon University.

The bottom line is that luck is the primary determining factor of when your hard drive will fail.  There some known risk factors, however.  A drive more than three years old has a much higher failure rate.  So if your important data is on a drive older than three years, be extra careful to make sure your data is backed up.  You may also want to replace an old drive.  Most drives more than three years old are much smaller and slower that what you can buy today for far less than you paid for the old drive.

Also, handling can cause hard drive failure.  Banging your computer around, especially when the computer is running (and the drive spinning) is a bad idea.  Also, dropping a drive just a couple of inches onto a table can cause or accelerate failure.