Recovery, however, shouldn’t be confused with easy. “Recovery is the thing that enables hard training,” Dixon says. If you’re rested and fueled, you can you push yourself to new heights in key workouts and increase fitness. -The Recovery Approach
This is a good article from Running Times- you can bet that many of us have at one time or another have been carried away by counting weekly miles, or like my weekly sub 7 minute miles.
Doxon's 4 pillars include endurance, recovery, nutrition, and strength. You can bet those key workouts he's talking about are brutal.