Its not if its when your hard drive will fail. (crash)
In the last two weeks I and one of the businesses I work for have had hard drive crashes. I had 90% of my data backed up, but the business had nothing saved. This company has now learned you must back up all important files. I have now installed a solid state USB external hard drive on their computer. They are backing up manually every time a major file changes, but a safer way is to use a program to do the back up for you. A good program to use is "Second Copy" Find it HERE
There are other back up programs to choose from, so shop around.
If you do not want to spend the money for automatic software and you are a dependable person you can do the back up in just a few minuts. Make the back up on a schedule. I do this each time an important file changes (like my checkbook) and once a week on Monday of the rest of the stuff. (like My Documents)
Please take my advise, back up your stuff !
Above Image from Gisbot