It's true. If you don't back up everything important you keep on your computer, you can lose it all. Back up everything you don't want to lose.
I started keeping all of DH's many medical appointments, treatments, etc. recorded on the wall calendar after he bacame disabled. And boy, was I grateful I had done that (and kept the calendars) a couple years later when Social Security reevaluated his disability status and wanted all those details...I could never have remembered all that otherwise. I gave them such a long and detailed list that there was no way they could fail to declare his disability permanent.
