Considering it seems such an obvious thing to do, it begs the question, ‘Why hasn’t someone done it before?’ I guess it comes down to two things: The physical strain of running such a distance and the ridiculous time commitment required to complete it. However, there may also be an important third reason… Forrest’s run is a work of fiction and that the actual film is quite vague as to the specific details. Furthermore, the book upon which the film is based (Forrest Gump is a 1986 novel by Winston Groom) doesn’t actually feature the run. The run sequence was a new creation by the film company (Paramount Pictures). All we have to go off is the seven-and-a-half minutes in the film, which includes how long he ran for and a blurred map that features behind a TV newsreader. And that only covers his first two years… after that it gets even more vague!
Full article: http://www.inov-8.com/blog/real-life-forrest-gump/