Backing up Your Files To a great extent, the value of your computer is actually the value of the work you have stored on it in the form of documents, spreadsheets, etc. While you can always replace a computer, it is often impossible to replace your work. The single most effective way to preserve your data is to back it up. Backing up means that you have more than one copy of your files in case something happens to the original or the computer. It might not even be a hardware failure you could make a mistake and accidentally delete a document.
Hard drives are much more reliable than diskettes.
Hard drives don't fail often, but it does happen as it can with any mechanical device. Some other part of your computer, such as the screen, might fail and you can lose access to your work while it gets repaired. Computers can also be lost, stolen or dropped. If we've succeeded in scaring you, good. It's a lot better to avoid the situation entirely, rather than having a panic attack once something has gone wrong and nothing can be done.