A key to successful backup and recovery is knowing that you have actually lost data. Somehow - I don't even know how - I deleted a file a couple of months ago (not critical, but something I wanted to have). When I went to find it today, it was gone.

Of course, all my backups over time dutifully copied the folder with the missing file. My last shot at it was finding the old data hard drive I replaced a few months back and mounting it. Unfortunately, being a good computer security person, I had apparently scrubbed it down to the metal back then.

If you don't know that you've lost data, you stand a good chance of eventually wiping that file out on your backups if you back up like normal people do on a daily basis.

Professional industrial backups keep huge rotating archives of each backup separately, so you can go back two years and find the exact backup of that time. I don't.