This is the "Ken Rideout Principle".
Ken went from a 3:30 marathon (8 min miles) to a 2:30 (5:43 min miles) without any coaching.
All he did was run a minimum of 10 mi every single day for several years.
Ken has since run a few sub-2:30 races and won the Master's division at the World Marathon Majors. @KenRideout_