Back in '98 or so, my mom asked me to help her troubleshoot sending a fax with her fax modem. We live on opposite sides of the state, so she called me to up help walk her through it. At the final step -- clicking "Send Fax" -- she said, "Okay, I just clicked it, and now nothing's happening. This is just what happened last time."
I said, "Uh, mom, the last time you sent the fax, were you also using the phone?"
"Yes. Why?"
"Because the fax modem can't use the phone line while you're talking on the phone."
She was more than a little embarrassed. But she's come a long way. One of the more-recent support calls I got from her was to seek tips for effective war-driving.
I have another story to share, but I don't have the time to type it up right now. Instead I'll keep you all in suspense.