To prepare for the role of the overweight character Mark Whitacre, Matt Damon purposely gained weight prior to filming. He did this by eating lots of hamburgers, pizza, and dark beer, which he described in an interview as being "really, really, really fun."
Whitacre mentions watching a show in which a character calls home and hears himself pick up the phone. This was the plot of a 1985 episode of The New Twilight Zone named "Shatterday", written by Harlan Ellison, directed by Wes Craven and with Bruce Willis as the guy with a double.
Whitacre's internal monologue about a great idea for a TV show where a man calls his house and hears himself answer the phone is part of the plot of Steven Soderbergh's own movie Schizopolis (1996).
Mark Whitacre is interviewed by John Dowd, who was later retained as an attorney for Donald Trump during the investigation by Robert Mueller into collusion between the 2016 Trump campaign and Russia.
This story was the subject of the 9-15-2000 episode (#168) of This American Life entitled "The Fix is In."