If It Ain’t Broke In “I” Mode…

I’ve worked in IT almost my entire life. This takes place in the mid-1980s when I’m working at a computer store. I receive a phone call.

Me: “Hello, you are calling [Store], [My Name] speaking. How may I help you today?”

Man: “My computer won’t work. The screen is just blank.”

Me: “That’s strange. Can you te—”

The man cuts me off.

Man: “It works in ‘I’ mode, but not in ‘O’ mode.”

“I” mode and “O” mode?

Me: “If it works in ‘I’ mode, then just keep it there, sir.”

Man: “Thank you! You’ve been a huge help!”

The man hung up.

How did this dude not know that “I” stands for “on” and “O” stands for “off”?