I agree with this phases thing.
I started without having any idea what I was doing but there was a few of us at school at 16 who were inspired firstly by the Coe/Ovett/Cram rivalry but also by the incredible marathon talent that was around at the time.
I now cringe at some of the 'training' we did but if nothing else we had determination....I'm sure I hit the wall a few times in training, thinking it was normal to have to 'go through the pain barrier'. Anyway, the end result was a rather shambolic 4:12 marathon at 16.
There was no internet to learn from and magazines didnt teach you much, but trying to use what little logic I possessed I then got the time down to 3:30 over the next 12 months. 3 marathons, 3 painful collissions with The Wall!
I then left the marathon alone for a while to concentrate on shorter stuff. Then a few years later it struck me that for a 17 year old without a clue 3:30 wasnt at all bad.
It was then that I underwent some postal coaching by Frank Horwill and the next 3 marathons were 2:52, 2:51 and 2:48 just through putting the right building blocks into the training.
The 2:48 was actually a major disappointment as the Horwill approach had got me fitter than that, probably about 2;35 fitness, but because I felt as fit as a fiddle I stormed off at 5:04 for the first mile and was actually leading the 2nd biggest marathon in the country at the time....... not what you would call a conservative, sensible start to a marathon. A 1:18 first half was followed by a painful 1:30 second half. Just when I thought the Wall had been left behind years ago it was back with a vengeance!
But it is these experiences that really teach you how the body works and you also learn that you can quite easily leave off the mileage for a few weeks/months without harming your 'potential'.
So, for me coaching is the provision of information that I can disect and think about rather than being handed a schedule as such.
I also agree that you will after a while need something to renew your enthusiasm and that is often an extended break. Even if it feels like it is wasting some of the fitness that has been hard gained you still have to work on the principle that the body knows when it needs a longer break than usual and this will often show up as disillusionment.
Top class waffling there!! 
Edited: 30/04/2010 at 16:21