关门养虎，虎大伤人

Explanation: Connivance encourage bad bad analogy, in the end their victimization. 　　Source: Qing Qian Cai, "said Yue Fei," says the forty-back to the ancients 'close support Tiger, tiger, Great hurt'. This thing, how they grow too familiar. " 　　Examples: The ancients said, 'close support Tiger, tiger, Great hurt'. This thing, how they grow too familiar. (Qing Qian Cai, "said Yue Fei," forty-back)