beginner's luck
noun [ U ] uk/bɪˌɡɪn.əz ˈlʌk/ us/bɪˌɡɪn.ɚz ˈlʌk/
新手的好运气
unexpected success experienced by a person who is just starting a particular activity
When I won the first contest I entered, he put it down to beginner's luck. 我第一次参加比赛就获胜了，他认为这是新手的好运气。