Tao is good at using it

A good traveler leaves no tracks.  
A good speaker makes no slips that can be criticized.  
A good counter does not need tally sticks.  
A good door-closer needs no bolt, yet no one can open it.  
A good knot-tier uses no rope, yet no one can untie it.

So the sage is always good at saving people, and therefore no one is abandoned.  
He is always good at making use of things, and therefore nothing is wasted.  
This is called hidden wisdom.

Good people are teachers to those who are not good.  
Those who are not good are lessons for good people.  
If you do not respect your teacher, or do not value your lesson, then even if you think you are smart, you are deeply confused.  
This is the essential, subtle truth.