天使的心里住着恶魔恶魔的心里只有天使
[tiān shĭ de xīn lĭ zhù zhe è mó è mó de xīn lĭ zhĭ yŏu tiān shĭ]
Suggests duality in character - inside a seemingly virtuous person hides a mischievous self whereas behind bad intentions lies purity or innocence. Reflects the yin-yang nature where good & evil coexist.