hit or miss
碰运气，凭运气，凭运气好坏来决定事情的结果
口语·凭运气决定
英文释义
unpredictable or haphazard, with a high degree of chance involved
例句
Finding a parking spot downtown is always hit or miss.
典故来源
与hit and miss同源，强调随机性和运气成分。