I've been asked several times how fast I plan to finish the marathon. I have no aspirations of qualifying for Boston or New York, so the time is ultimately immaterial. I do, however, have a plan.
At first I thought 4 hours would be a good, feasible goal. It was fine until I worked out the math and realized this is a 9-minute mile. I can absolutely do 9-minute miles, but 10-minute miles feel a lot better and a lot easier, especially as the mileage increases. If I can maintain a constant 6 mph I'm looking at about a 4.5 hour marathon. If it becomes 5 hours, that's fine too.
In the end, regardless of whatever time I'm aiming for, the only thing that matters is finishing. If I get to 18 or 22 or 26 miles and my body shuts down, it's ok to walk to the end. My goal is to cross the finish line by my own power, regardless of how long that takes.