Running a marathon is no easy task, and being able to say that you did it is something pretty cool. The reality is that just about any human that trains can run a marathon. No, it's not easy, and it takes a lot out of you, but you can do it, I know because I did, many times. Of course, I had a little bit of help, I had some good coaches, and I had some very good reference material.
If you are considering running a marathon, then I know the very good book that you should probably read. I do own this book personally and I've had it for a good 35 years. The name of the book is;
"Target 26; A Practical Step-By-Step Preparatory Guide to Running a Marathon," by Skip Brown and John Graham, Collier Books, New York, NY, 1979, (251 pp), ISBN: 978-00202-8820-6 .
The authors discuss all the important items such as training and diet. They also discuss the stress on the body, the potential for injury, and the reality that you must take your training step-by-step without pushing yourself too hard causing an injury or sickness. There is also a good chapter on running shoes, attire, and equipment. Especially if you have to train in cold-weather or in the rain, and yes, you have to run every day so there are challenges of training.
The authors also talk about the race and your performance. They suggest various strategies for different types of runners and why you must work on maintaining your conviction to improve your personal best. They suggest ways of recordkeeping and race improvement towards the end of the book, and I'm thankful to say that this book helped me run several marathons under three hours. These consider all this.