There was a time when movie directors had to start out in the movie industry and work their way up. Alfred Hitchcock started out as a title designer. John Ford started out as an assistant to his brother Francis. In the old days, if one wanted to direct films, he or she had to either work his way up to it or have a relative already in the business. Or both.
All of this changed with the advent of regular network television broadcasts in the late Forties. No longer would anyone wanting to be a film director have to start in the film industry. Now he or she could find his way into film direction by way of directing television. Indeed, several big name directors have had their start in television.
Among these was Sidney Lumet. Lumet started out as an actor, but he eventually found himself at CBS directing episodes of such series as Studio One and Danger. He broke into film in 1957 with the adaptation of a teleplay by Reginald Rose. Twelve Angry Men had first aired in 1954 as an episode of Studio One. Lumet would continue his work on television for a few more years, until he abandoned it all together after directing the movie Long Day's Journey into Night. He would go onto make such films as The Pawnbroker, Fail-Safe, and Serpico.
Sam Peckinpah also started in television. In fact, he started as a lowly stagehand on The Liberace Show in 1952. By 1955 he was a writer for Gunsmoke. Two years later he would create the classic Western series The Rifleman. He would both write and direct episodes of the show. He would also create the short lived series The Westerner, episodes of which he also wrote and directed. Fittingly, given his work on Western TV series, Peckinpah's break into film came with a Western--the classic Ride the High Country in 1962. Within a few years Peckinpah would be firmly established as a film director, directing the classic Wild Bunch.
Perhaps the biggest name in film direction to emerge from televison was Steven Spielberg. After serving as an assistant editor on Wagon Train and making various short films, Spielberg entered the field of direction with one of the segments for the pilot to Rod Serling's Night Gallery. He went onto direct episodes of Marcus Welby M.D., The Name of the Game, and Columbo. It was directing the telefilm Duel, however, which really got him noticed. First aired in 1971, it was one of the most successful television movies of all time. Spielberg broke into the movies in the biggest way possible. He directed one of the biggest movies of all time--Jaws. The film was the hit of 1975 and the highest grossing film of all time until it was surpassed by Star Wars Episode IV: A New Hope. Since that time he has been one of the most successful directors in the history of film.
Since the Sixties it has not been terribly unusual for television directors to eventually make the move to film. Paul Haggis, Mike Newell, Michael Mann, and many other movie directors got their start working on television. Even Tim Burton, better known for his early animated shorts, did some work in TV. In 1982 Burton directed a special for the Disney Channel entitled Hansel and Gretel. Based on the fairy tale of the same name, it was done in the animated style of The Nightmare Before Christmas. In 1984 he directed an episode of Shelly Duvall's Fairie Tale Theatre entitled "Aladdin and His Wonderful Lamp." Of course, during this time Burton was also working on Disney's various animated feature films (The Fox and the Hound, for example).
There was a time long ago (the Fifties) when television was regarded by the film industry as a bitter rival. Today it is simply one of any number of media. Given the number of film stars and directors (and in some cases both in the same person--Clint Eastwood started in television) who have emerged from television, the film industry couldn't resent it for long.