Most sportsmen and women, no matter how high they progress up the professional ladder, do what they do because of a deep-seated love of their sport.
Marathoners are different. Even those with a masochistic streak reach a point in the race where it just stops being fun. That old maxim about a fine line between love and hate is at work here.
"At 20 miles [32km] you really want to be done. It's not very comfortable at that point," says Kimberley Smith, who tomorrow will line up on The Mall to run the gruelling 42km race.
"It's a really painful race. Not a lot of fun."
London will offer a flat, possibly fast race, although the 11am start and the potential to be running through the hottest part of the day might militate against scorching times.