三十辐共一毂，当其无，有车之用。
Thirty spokes meet at a single hub.
It is the hole at the center that makes the cart useful.
埏埴以为器，当其无，有器之用。
Clay is shaped into a vessel.
It is the emptiness inside that makes the vessel useful.
凿户牖以为室，当其无，有室之用。
Walls are cut for doors and windows.
It is the openings that make the room livable.
故有之以为利，无之以为用。
So: what is there gives you the advantage.
What is not there gives you the use.
Reading it
Three examples, one point: the made thing is the frame, the gap is the function. This is the most concrete argument in the book and the easiest to apply to a life. A calendar with no gaps is not a full calendar; it is a broken one, because nothing can be put into it. The same holds for attention, for conversation, and for a room.
Find one thing in your week that is full and take a quarter of it out. Do not fill the gap.