A marathon is 42km. Running it every month is equivalent to impossible for most.
1 month has about 30 days. Minus off the weekends we have 22 days. If we’ve just run 2km every weekday, we would have ran 44km.
We’d have even exceeded the distance of a full marathon.
Run a marathon every month using this method and you’ll be running 12 marathons in a year.
Because, why not?