Just to prove that the advice here is true - here is my little story of success.
When i first started running three weeks back, i could barely run 100 yards without being out of breath and my legs caving in.
The first time i went out i felt a right loser, and almost never carried on training.
I'd just kicked a 40 a day habit and my lungs were a mess.
Now, its only 3 weeks on, but after swimming, rowing, cycling etc at the gym, not to mention the 3 nights a week ive been running.. on thursday last i finally noticed the real difference. I went down the usual way i go, and realised that i was where i normally stop, and i felt ok.. so i figured i'd press on a little until i hit that usual stopping point.
Well, i got to the edge of the cycle track, and still i felt ok, not great, but ok- i knew i could continue albeit at a far reduced pace.. so i took a wee walk break (fast walK), and when i felt a bit better, broke into a slow jog.. i ended up doing a full circuit of the block...
The final 1/2 mile, was the worse, my legs were aching, i could feel the burn in them, first time in ages.. i actually felt the warmth coming off them, and my lungs were crying out.
I slowed to a fast walk, then a normal walk, then a slow walk and before long was at my front door. I did my cool down stretches etc and felt very impressed.
I checked on the map, and it was about 2.5miles.
Now, may not seem a lot, but for myself who'd just kicked a 40 a day habit, and only 3 weeks earlier wasnt able to run 100yards, i feel thats a massive improvement. All achieived by merely spending time on my feet, walking, running, jogging, walking again etc..
Still dont know how on earth im going to manage 26.2mi next year though if im successful.