《庄子·外篇·知北游》
锻制带钩这是得用心专一的事，借助这一工作便不再分散自己的用心，而且锻制出的带钩得以长期使用，更何况对于那些无可用心之事啊！
是用之者假不用者也，以长得其用，而况乎无不用者乎！
Making belt hooks requires undivided attention. This work helps me to concentrate my mind, and the belt hooks I make can be used for a long time, not to mention those things which are not worthy of undivided attention!