The town I live in organised a 10k run for local funding. Mrs Kingdom suggested we both do it, as it turns out I ended up doing it on my own. I started really from scr, hadn't done any form of training in about 5 years and the lumps were well showing. There was a meet and train group, with a coach and really it was baby steps from the first day. I love sport but have always hated running just for runnings sake. I was a mess on the first day, puffing and ruined after 1 x 700m lap of the trail. We seemed to be doing very short distances, lots of stretching etc, but after about 4 weeks (only 3 x 1hr sessions a week) the fitness really improved, so much so that he surprised us into doing a 7k run one evening, and couldn't believe how easy it was. I had hoped to do the 10k in under an hour (not really an achievement - but from the starting point it did not look realistic).
We were very lucky insofar as the course was well mapped out from the first days training. The day itself was tough, it was hotter than anything we'd trained at, and the course itself took in a very steep hill right in the middle of the course. I was very happy with how it was going and three of us had grouped together and that was a massive difference. However the finishing line was changed on the day (something I wasn't aware of) and all the motivation of "keep going - only this corner to go" completely went when I realised the finishing line was another 500m away. It was like someone had stuck a blade in my back, couldn't believe afterwards how badly it affected me. I literally stopped in the street, and it took at least a minute for me to get going to do the last half kilometre.
I know it's not a marathon but it's giving an idea of the mental aspect that I would have scoffed at previously. I was very happy to do it in 57:53, achieving the goal. I'll keep doing them and then consider the big one in a couple of years.