" In the zazen posture, your mind and body have, great power to accept things as they are, whether agreeable or disagreeable.
In our scriptures (Samyuktagama Sutra, volume 33), it is said that there are four kinds of horses: excellent ones, good ones, poor ones, and bad ones. The best horse will run slow and fast, right and left, at the driver's will, before it sees the shadow of the whip; the second best will run as well as the first one does, just before the whip reaches its skin; the third one will run when it feels pain on its body; the fourth will run after the pain penetrates to the marrow of its bones. You can imagine how difficult it is for the fourth one to learn how to run! "

― Shunryu Suzuki , Zen Mind, Beginner's Mind: Informal Talks on Zen Meditation and Practice