In the days of paper tickets, I had a late morning return from IND but apparently I mistook the flight number for the departure time when checking my ticket. I had a leisurely drive to the airport, filled the tank and returned my rental car, but then noticed that my flight wasn't listed on the airport monitor. When I arrived at the check in counter to ask about the cancellation/delay, the flight was gone: Flight #1150 at 1015 am or something similar.