He became stronger after going through a rough patch when he lost his job.

a 是不定冠词，表示"一个"或"某种"。 rough 的意思是"粗糙的"，引申为"艰难的"或"困难的"。 patch 本义是"补丁"，引申为"一段时期"或"阶段"。 a rough patch 指"一段困难时期"，比喻生活中遇到的艰难阶段。