"Back to zero" is when you receive an order, make the product, deliver it and take payment. It's like buying land, building on it and then selling it. At then end you have nothing in your hands, and just have to start over.
所謂歸零，就是你接到訂單，生產產品、送貨，收帳；又比如土地買來，房子蓋了賣掉，就沒有了，一切重新再來。