The most comical part of marathon training is that you have to run 20 miles...in order to 26 miles. In order to complete the maximum goal, you need to complete 80% of the distance multiple times. It'd be like winning 80% of the Super Bowl three times before being able to play and win it for real.
Nevertheless, 20 miles just for fun allows for an entire afternoon of guilt-free eating. With 2000+ calories burned, I have an entire day's worth of food ahead of me before I even break even. Time to get started!