Both distances are challenging. Training for and running a fast mile is intense with lots of speed intervals on tracks needed to pr. Marathon training can't be properly done without months of scheduled training and the absolutely essential long runs of 18 to 24 miles which pretty much wipes you out for that (usually weekend)day. I don't perform well in either discipline, my sweet spot is 10 k to half marathon. Lots of awe and respect to those who do well in those events....Is a sub 2 marathon humanly possible? Seems out of the realm of human possibilities but so did a sub 4 mile for over a hundred years!