Has the drive been rather slow or maybe acting a little weird recently?
How old is the drive?
how often is the drive in use, and is it often left to idle for long periods of time?
That all being said Drives do eventually fail, yes it sucks alot but this is why you must keep a backup or your important data.
Believe me, I've lost a drive full of data before and had no backup. Now I keep a backup and have it update the image evrey week.