First of all, it helps to be familiar with the Tommy Westphall Universe Hypothesis. Tommy Westphall was a very minor character in the 1980s TV show "St. Elsewhere". Tommy was the son of Dr. Westphall, the Chief Physician at St. Elegius, the fictional Chicago hospital that is the setting for the series. I'm not sure if Tommy even appeared until the series finale, but on the show it was always known as a background fact that Tommy had Autism. At the end of the series finale, it is revealed that all of the people and events of the entire series had taken place within Tommy's imagination. In a nice added touch, Tommy's father, we'd have to call him Mr. Westphall I guess, is shown to be a janitor.
From this ultimate plot twist, enthusiastic pop culture nerds have developed the idea further. Noting that occasionally, "St. Elsewhere" characters had done "crossover" episodes on other NBC shows … presumably as a gimmick to boost viewership … and noting further that those shows had shared character crossovers with still others … then it stands to reason that Tommy Westphall's internal "universe" actually encompasses a large percentage of fictional television.
It's all fun and a bit silly. Still, I think that something like this may be at work in our understanding of "Forrest Gump." I'm not suggesting that the entire story is made up in Forrest's mind. I'm saying that it's possible to accept the broad outlines of the story, while considering the possibility that Forrest's enormous, almost supernatural good luck is in part a function of how Forrest understands his own experience.
In the movie, Forrest is understood to be mildly cognitively impaired … or "mentally retarded" in the old terminology. His mind clearly isn't altered enough for him to have dreamed up the whole story like Tommy Wesphall, but maybe enough to bend and warp the nature of his own role and place in the events of his life. In the places where we say to ourselves, "How could that really happen?", maybe the answer is, "Maybe it didn't happen exactly like that", or, "We don't know how it happened because Forrest really doesn't, and we're seeing all of this as Forrest does."
That's what I meant when I said that "Forrest Gump" can be viewed in part as a simulation of what it's like to be Forrest. We don't just see what happens to him, we see things as he sees them, filtered and perhaps changed though his unique mind. It helps explain the movie's extraordinary strokes of luck and improbable coincidence, as Tommy Westphall's savant imagination sheds light on why events and characters on "St. Elsewhere" had become gradually, subtly stranger as it progressed. But while the Tommy Westphall phenomenon was an explicit and intentional plot point, this "Forrest Gump Hypothesis" is just speculation, and probably wasn't an intentional thing.
Intentional or not, I wonder if the simulation of cognitive impairment we seem to get in "Forrest Gump" is realistic. I also wonder whether there are other movies or TV shows that don't just depict people with cognitive impairments, but try to put is in their shoes ... and in their minds?