The success of his first restaurant was just 'beginner's luck'. [=he succeeded because he was lucky, as beginners sometimes are]
a swimming class for complete 'beginners' = a 'beginner' class
(..) I'll go get one. When you told me to get this baby out for you... I thought my hearing was going. I says to myself, Leon's a pro. Nobody uses that except beginners I like to stay in shape. Sure. Always stay on top of it. It's like me. I gotta know where everything is all the time. (..)1994 Léon: The Professional