Intellectually challenged savant, accompanied by a rag tag gang of miscreants which include, his drug addicted temptress, his black man servant with a severe speech impediment, his atheist physically handicapped roommate, and his overbearing mother who strongly resembles Carrie from Smokey and The Bandit, uses his magical storytelling powers to alter events in history to change people's perception towards how those with disabilities can contribute positive value to society.
This movies also takes several indirect, yet highly offensive jabs at professional basketball player Earvin "Magic" Johnson. During the film, Jenny, the heroin addict with more baggage than a Southwest Airlines $199 Labor Day weekend special on domestic flights, decides to travel to San Francisco in a van with questionable group of hippies after S.H.I.E.L.D enlists Forrest to go all Hulk mash on the current black panther movement gaining momentum. One can only logically deduce that during her time San Francisco spent laying around in seedy motels doing intravenous drugs, somewhere in one of her bouts of intoxication one of her dealer boyfriends must've enjoyed following games by the 80s Showtime L.A Lakers starring Magic Johnson, Kareem Abdul Jabbar, and James Worthy, and she became a following the games by osmosis as she lay there in a heroin trance state. She begins following basketball games as a means of escapism, and becomes so enthralled in the sport that Jenny begins using this as a distraction to fuel her sobriety.
It can only be assume that at some point during her tenure in San Francisco, she eventually meets up with and has sex with Magic Johnson while he's in town for a road game against the Golden State Warriors, and subsequently contracts aids. Ashamed and sick, she decides to go back home to Alabama to be supported by her millionaire shrimp boat captain classmate.
There might be some holes in that theory.