There was a time in college and after college where I was totally dedicated to running.
And I could not conceive of getting in a single 100 mile week.
My highest total ever was 74 miles in a week. My longest single run was 12 miles.
That was training for the 1500.
There were some fast runs and workouts thrown in there which made it tough to pile mileage onto.
But even in a early spring base week with simply distance runs, I could not approach 100 miles.
I remember talking to Darrell General who qualified for a few Olympic Trials marathons and he only ran 70 miles per week on average.
Of course he did that while working.
Anyway, I found 100MPW to be that hard.