俱舍論記 15.89

15.89

「住惡戒者至病終難愈」者，明惡戒易得，有誓受得。惡戒難捨，捨事不捨，要得善戒方能捨彼。喻況可知。

"One who abides in bad discipline [...] the illness is ultimately difficult to cure" explains that bad discipline is easy to obtain, being obtained through vows. Bad discipline is difficult to relinquish; relinquishing the action does not relinquish it, and only upon obtaining wholesome discipline can one relinquish it. The simile is understandable.