Looking for the title of a french movie

There's a french movie about some loser in Paris who has a shitty job and can't get a girlfriend. He meets a handicapped writer in a bar who is prepared to script his life. He tells him to do one thing he normally would never dare to do - every day. This makes him hugely succesful. What is that movie called? I think it's from the 70's, but I can't be sure.