When is Enough, Enough?

I was on the phone about a week ago with an old friend and was asked about my plans for racing this year, to which I replied "Oh Boston in April and Hardrock in July." In my world these are two kids on different sides of the playground when it comes to running. 2017 will mark my 5th Boston Marathon and it will also mark my 4th Hardrock, a 100 mile trail race in Silverton, CO that takes place above 10,000 feet. So my friend then says to me "Do you ever ask yourself, when is en