It was never going to be easy, but it's just been made particularly hard for Mo Farah as he prepares for his marathon debut in London.
A super-elite field has been announced this week with the world's best marathon runners all queuing up to take on the British Olympic star over the distance on April 13.
Farah is aiming to become the first British man to win the race since Eamonn Martin 21 years ago and, for all that he has already achieved in his illustrious career, this represents somewhat of a career crossroads.
It will not be until after the marathon that Farah and his camp begin to make a firm decision on his targets and goals for the remainder of the year, and the race could well dictate the direction of his career from this point onwards.
As has been admitted by the double Olympic champion, so far there are no definite plans regarding competing on the track at either the Commonwealth Games in Glasgow or the European Championships in Zurich later this year. A great deal is going to be on the line.
His ambition of translating his dominance over 5,000 and 10,000m to the significantly longer distance of 26.2 miles is admirable, but is it attainable against such seasoned specialists?
To invest so much time and training in adapting to a very different event is always going to be a big risk, but under the tutelage of three-time New York Marathon champion Alberto Salazar he is going about his work in the right way.
Farah completed half last year’s London Marathon as a training run but taking on such a high-quality field this time around will be an entirely different proposition. He gained valuable experience last April, but this time the intense pressure and the expectation will engulf him.
Lofty ambitions always come naturally to the great athletes, and Farah is probably the greatest Britain has ever produced. But to move serenely to tackling the marathon distance against the world's best is a challenge that is hard to overstate.
Even eclipsing the British record of 2:07.13, set by Steve Jones 29 years ago in Chicago, will not come close to challenging the world's best if they are at the top of their game.
Six runners in the field announced for the London Marathon have gone under 2:05. Emmanuel Mutai will be present - the Kenyan star who set the course record of 2:04:40 three years ago.
Also in the field are Geoffrey Mutai, who has run the fastest - albeit not officially recognised - marathon in history, Wilson Kipsang, the world record-holder, and Stephen Kiprotich, the Olympic and world champion from Uganda. Oh, and Ibrahim Jeilan, the Ethiopian who beat Farah to gold in the 10,000m at the World Championships in Daegu in 2011, and last year's winner, compatriot Tsegaye Kebede.
As Hugh Brasher, the London Marathon race director, said: "Much attention in Britain will focus on the performance of Mo Farah and we are very pleased that he has chosen London to make his marathon debut.
"But it will be an extremely tough challenge for Mo with the quality of the elite field as high as ever." Again, that's an understatement.
Farah has admitted that competing for glory at the London Marathon was a boyhood dream and it would represent a quite stunning career development for the athlete.
"I am expecting it to be one of my toughest races and a real learning experience," the 30-year-old said. "I gained a lot of valuable experience running part of the course alongside the top guys last year and can’t wait to race over the full distance this April.
"The London Marathon always attracts the world’s best runners to its elite fields and this year will be no different. I had another great year on the track in 2013, but the marathon is my main focus for this year.
"As a young boy growing up in London it was always my ambition to run the London Marathon, and to be able to make my marathon debut in my home town is very special."
As for his plans until April, Farah is to continue his intensive training in Portland, Oregon before embarking upon a period of high-altitude work in Kenya later this month.
He may end up having endured a chastening experience in what is his first competitive marathon, but the risks are surely far outweighed by the potential of confirming his status as arguably the best all-round athlete in the world.