《韩非子·难三》
事情中称得上困难的，一定要给予人家权力来形成威势，却又不想让对方侵害自己，这可说是第一件困难的事。宠爱纪妄，却又不使她与正妻地位相等，这是第二件困难事。
物之所谓难者，必借人成势而勿侵害己，可谓一难也，贵妾不使二后，二难也。
What can be called difficult in this case is definitely giving someone power to increase their power, yet not wanting them to harm oneself, this can be called the first difficult thing. Pampering Ji Wang, yet not making her status equal to the main wife, this is the second difficult thing.