If your mind is clear, true knowledge is already yours. When you listen to our teaching with a pure, clear mind, you can accept it as if you were hearing something which you already knew. This is called emptiness, or omnipotent self, or knowing everything. When you know everything, you are like a dark sky. Sometimes a flashing will come through the dark sky. After it passes, you forget all about it, and there is nothing left but the dark sky. The sky is never surprised when all of a sudden a thunderbolt breaks through. And when the lightning does flash, a wonderful sight may be seen. When we have emptiness we are always prepared for watching the flashing.
— Shunryu Suzuki (in Zen Mind, Beginner’s Mind)