Twice The Running Does Not Give Twice the Return
The basis for all training is that an organism exposed to stress will adjust (and get stronger or faster) if able to recover. But if the organism never rests, it just stays tired. The goal is always to get the best results from the least effort. Twice the running will not provide twice the return. Counting miles for the sake of counting miles is a dead-end.
There is an inherent trap with high mileage. The only way to get them is by running a lot of miles every day — which can overtax the runner if they do not allow themselves breaks, but taking breaks hurts the overall weekly mileage.
As much as we may like the thought, the hardest worker doesn’t always win, more times the victor is the smartest worker. Train, don’t strain. The winner is the athlete who improves the most, not who does the most. The aim is to find the optimal balance of work, rest and race, not the most difficult training regime possible.