I don't know if it's a prioritization thing or a psychological thing, but I have yet to fill out my training plan completely, either in my RunningAhead.com Training Plan or in my Google Docs spreadsheet.
Last week featured back-to-back 11 and 13 milers, ending with a 15 miler at the end of the week.
Wednesday (tomorrow) and Sunday this week and next feature a 14 miler and an 18 miler. Those seem pretty daunting at this point.
It's not the distance or weekly volume that has me apprehensive. I've went as far as 23 miles in training runs before. My plans have peaked with a few consecutive weeks around 80 miles per week. With this plan, my first 20 miler is still weeks away, and the plan peaks at 70 miles per week.
One difference is that this plan is structured differently: My former (often improvised) 80+ mile plans consisted of lots of "doubles": 2 runs in a day. It's a little easier to squeeze in workouts when you do 7 miles, 5 miles, etc... then one 20 miler. I'm also trying to stay fairly faithful to the up-tempo and marathon pace long run schedule (so far).
Another possible difference is that my work and family schedule have made me favor (almost exclusively) the early morning run. I was doing outdoor runs for some of those, but the excessively humid air on the one cool day in the middle of a long hot streak was so laden with gnats that I really haven't had the interest in getting back out there in the darkness until it cools off a little.
That leaves me running on the treadmill, and for the interest of time, the treadmill downstairs.
For 2+ hours.
Twice a week.
Maybe I'll venture outside tomorrow morning.
Two 2+ hour runs on a treadmill in the same week.