The phrase is traced in modern usage to drama theorist
洪深 (Hong Shen)'s 《
电影戏剧表演术》 (Techniques of Film and Drama Acting, ch. 3):
表演的所以能感动人,
就是因为演员的诚恳,
所谓'
假戏真做' — 'What makes acting move people is the actor's sincerity — what we call jiǎxì zhēnzuò.' Originally a praise of actors who fully commit to fictional roles.