This one time, I was playing a game online. Ah, the days when I knew next to nothing about computers...
I was in the in-game chat rooms, and had asked a technical question about my computer. Someone in chat responded with some guidelines. I replied, "Cool, thanks! I'll give that a try."
In my naivete - bless it - I took his advice and ran the command lines he told me to try... AND FORMATTED MY HARD DRIVE. Thankfully my dad knew how to reinstall Windows at that time, so I was back up and running in a day or two.