premise: Sean Penn is only ever a stage actor.
hypothesis: Sean Justin Penn ( born August 17 , 1960 ) is an American actor , filmmaker , and political activist . Penn began his acting career in television with a brief appearance in episode 112 of Little House on the Prairie ( December 4 , 1974 ) , directed by his father Leo Penn. . Following his film debut in the drama Taps ( 1981 ) and a diverse range of film roles in the 1980s , including Fast Times at Ridgemont High ( 1982 ) , Penn garnered critical attention for his roles in the crime dramas At Close Range ( 1986 ) , State of Grace ( 1990 ) , and Carlito 's Way ( 1993 ) . He became known as a prominent leading actor with the drama Dead Man Walking ( 1995 ) , for which he earned his first Academy Award nomination and the Best Actor Award at the Berlin Film Festival . Penn received another two Oscar nominations for Woody Allen 's comedy-drama Sweet and Lowdown ( 1999 ) and the drama I Am Sam ( 2001 ) , before winning his first Academy Award for Best Actor in 2003 for Mystic River and a second one in 2008 for Milk .