[math-fun] September 10000, 1993

There's a bit of Internet folklore that says September 1993 never ended. (Look up "Eternal September" for details.) September 100, 1993 was otherwise known as Thursday, December 9th, 1993. September 1000, 1993 was otherwise known as Monday, May 27, 1996. September 10000, 1993 is today, otherwise known as Saturday, January 16, 2021. I thought about the pattern of the days of the week of the successive rollover days, and concluded that there's just one day of the week that they will never land on. Can you see which one, and why?