These two words are a source of trouble for many English learners.

对于许多英语学习者来说，这两个词是个麻烦。

As he now never enjoyed internal peace, the condition of his fellow creatures was to him a perpetual source of trouble and distress.

由于他现在从未享受过内心的平静，他的同胞们的状况对他来说永远是麻烦和痛苦的根源。