山中の賊を破るは易く心中の賊を破るは難し

さんちゅうのぞくをやぶるはやすくしんちゅうのぞくをやぶるはかたしsanchuunozokuoyaburuhayasukushinchuunozokuoyaburuhakatashi

expression

1. it's hard to discipline one's mind
2. defeating the bandits in the mountains is easy; defeating the bandit in one's heart is hard

Study it in Yanamino