It never rains but it pours.

(1) idiom:  It never rains but it pours. 禍不單行
(2) meaning:

Bad things do not just happen a few at a time, but in large numbers all at once. (壞事要不就是很少發生，要不就是一發不可收拾。)

(3) 說明：Never~從不，rain~下雨，pour~傾盆大雨