‘In the stillness (when we are sitting zazen) various kinds of thoughts arise and go away when we let them go.They disappear and only the wall remains in front of our eyes.We should be grateful to zazen, which teaches us that all kinds of thoughts fall off when we open our hands, and only the wall is left. We should understand this thoroughly. If we continuously practice, we will understand that various thoughts appearing in our mind are nothing but secretions of our brain.’ (The Wholehearted Way)
I have used Uchiyama Roshi’s observation about thoughts being the secretions of the brain almost every time I have done zazen instruction – it was so helpful to me to see this, and I hope it has a similar effect on all those who grasp it.