The next time I see Mr David Bedford I've got a bone to pick with him. I will be asking the Virgin London race director exactly what happened to his 21-mile marker back in April.

As a marathon virgin, I was happy to see the balloons and gantry clocks marking all the other significant staging posts on the long and winding road from Greenwich to the Mall, but I still find it scandalous that one of them should simply have been forgotten.

Well, I certainly didn't notice it.

I suppose it could have been my mistake.

But if it was my mistake – and that still doesn't mean I accept it definitely was – it would hardly be the first misjudgement to have been made under the rigours of the 26.2 miles distance. There are so many opportunities to err in the marathon, whether you are a novice, a club runner or even an elite international.

Indeed, if legend is anything to go by, the first marathon runner, Pheidippides, was guilty of an error in pace judgement so fundamental that he dropped dead upon completion of his race. You can't help but think a few well-timed drinks and gels might have been a good idea there.

The thing about the marathon is that it is like an ocean – full of infinite variety, almost too vast to encompass.

And when we witness someone mastering the distance in the manner that Paula Radcliffe did in running her world record of 2hr 15min 25sec at the London Marathon in 2003, there is the same sense of awe as when we watch a surfer riding a glistening-backed monster all the way to the shore.

Fast forward a year from there, and the same runner sits on a pavement, broken and tearful, in the heat of an Athens evening. Such is the power of the ocean.

At 37, and as a mother of two, Radcliffe is still responding to the call of the sea. Her confirmation this week as an Olympic selection for London 2012 means she will be partaking in her fifth Games – and, incredibly, looking for her first medal.

It would be glorious indeed were she finally to find her way onto the Olympic podium on home soil. But if that turns out not to be the case, she would unwillingly join an illustrious list of great runners who have failed to earn medals at the Games.

Take Jim Peters, for example. Another proud Brit who entered the Olympics as world record holder for the marathon – in his case, in 1952 – and came to grief less than 26.2 miles further on.

Peters, as was his wont, set off fast, but when Emil Zatopek, running his first marathon, moved up to him and enquired if the pace was good enough, he replied "Pace too slow" and upped his speed. The Czech passed him just before the halfway point en route to a debut victory, and the Briton collapsed with a quarter of the race remaining.

Two years later, having become the first man to run the marathon in less than 2hr 20min, Peters again misjudged the pace in the suffocating heat of Vancouver at the Empire Games, arriving at the stadium 17 minutes ahead of the field, but then tottering to an agonised halt with 200 metres remaining in what was to be his last competitive race.

Getting things right in the marathon is no easy task. Last month British runner Jo Pavey reflected upon the marathon debut she had made in London in April of this year, acknowledging that despite all her preparations she had found herself hitting the metaphorical wall at 17 miles – "It was like flicking a switch."

The experience of a debut marathon this year was not quite as dramatic for Scott Overall (pictured), who has been a British international at 5,000 metres for several years, also confirmed this week as the first British male runner to be taking part in next year's Olympic marathon. But it contained some classic misjudgements, the most serious of which, as things turned out, may have worked in his favour.

In a blog describing his debut marathon in Berlin this year, Overall describes how he set off with a group of pacing athletes who seemed to be ticking the box exactly for the schedule he had envisaged, only to realise after three kilometres that he was running alongside men due to go through the halfway point in 63min 30sec – which was a little faster than he required to achieve his Olympic qualifying mark of 2:12.

But the overly swift start suited Overall, as it turned out, albeit that he found the final five kilometres increasingly hard going. So much so that he made another basic error in calculation with two kilometres remaining.

"I worked out I needed to run eight minutes for the last 2km to get 2hrs 12min," he wrote. "However, I was thinking in miles, in my head I was thinking I need to run the last two miles in eight minutes, I couldn't do it."

What a nice surprise it was for him when he got within sight of the finish gantry and saw the clock saying 2:10 and something before crossing the line, somewhat dazed, in 2:10.55.

Overall also recalled how, having had a couple of "shocking" track runs in the US earlier this year, he had run the Indianapolis half marathon in 63:21, adding "it dawned on me that perhaps my future was on the roads."

He then recalls how a meeting with Dave Bedford ended with the former world 10,000m record holder insisting: "You have to leave this office as a marathon runner. No more track, from this point on you are a marathon runner."

Good advice from Mr Bedford. He knows full well that, where the marathon is concerned, full concentration is required.

Mike Rowbottom, one of Britain's most talented sportswriters, has covered the past five Summer and four Winter Olympics for The Independent. Previously he has worked for the Daily Mail, The Times, The Observer, the Sunday Correspondent and The Guardian. He is now chief feature writer for insidethegames. Rowbottom's Twitter feed can be accessed here.