se听则明 jian1 ting1 ze2 ming2 : grasp two things, listen, [as a] rule bright
偏信则暗 pian1 xin4 ze2 an4 biased beliefs [as a] rule [in] darkness
Listen to both sides and you will be enlightened;
heed only one side and you will be benighted.
In other words: listen carefully, hear both sides, think it over and the light bulb will turn on.
In contrast, bias, misplaced trust, but also distrust as a rule will lead to darkness.