hit-and-miss

剑桥词典

If something is hit-and-miss, you cannot depend on it to be of good quality , on time , accurate , etc.
没准的，碰运气的
The trains are often late, so getting to work on time is a fairly hit-and-miss affair . 火车经常晚点，所以准时上班在很大程度上是件碰运气的事。 返回 hit-and-miss