1. Not Enough Training Background
The first and perhaps most obvious reason you might not want to run a marathon is a lack of training or experienced running background. The marathon is an arduous event and requires a dedicated training block of at least two months for serious runners and four months or more for newer runners. Remember, the more time you give yourself to train for your goal race, the better your chances of success.
More importantly, training for a marathon when you don’t have the requisite running background is a surefire way to get injured or find yourself disenchanted with running if you’re new to the sport. In my experience as a coach, I’ve found that beginners need to be able to average at least 40 miles per week for 5-6 weeks to increase the chance that they will have a good race experience. This means that you need to be able to comfortably run 30-35 miles per week before you begin training for a marathon. If you’re not at this number, it doesn’t mean you can never train for a marathon. Rather, you should focus on slowly building your training tolerance and mileage background. Otherwise, you’ll likely struggle to increase the length of your long runs, as well your weekly mileage, enough to be adequately prepared on race day.
When runners neglect this advice, they often find themselves in a vicious injury cycle that is tough to break free from. First, the sharp initial increase in training results in a small injury that sets them back a week. To make up for missed time, they push the envelope to get back on track and develop another small injury. The cycle repeats itself throughout the entire training segment until race week, when a runner realizes they haven’t put together a solid, uninterrupted month of training since they started.
The last thing anyone wants on marathon race day is to have a bad experience and to suffer through the course. Even if your goal is only to finish, make sure you have the necessary running background to start marathon training on the right foot to stay injury-free and to have a good race.