It is far easier to remember to back up your files if you establish a regular routine for doing the backup. The regularity with which you do your backups depends upon how much you update files and create new ones. Because your time is too important to go through the process of thinking about and typing the same information more than one time. But you say you have never lost a file in all the years you have been using computers. You should count yourself among the lucky ones.
Computers are mechanical.
Eventually, one way or the other, they fail. Viruses infect files. When these natural and unnatural disasters occur, you want to be prepared. Think of it as redundancy. Think of it as insurance.