A Winning Script
While there were definite hiccups in finding the actors for the films key roles, they eventually convinced Tom Hanks to sign on for the film. They gave him the script and after reading it for an hour and a half, Hanks needed no further convincing.
According to Steve Starkey, producer of Forrest Gump, they sent the script over to Tom Hanks because he was the only actor left on their list who could play the role. After an hour and a half of getting the script to Hanks, the actor called them to say that he was in.