‘Ordinary people are out working so they carry on their daily lives without thinking that their own unreal thoughts are unreal. But try doing a little zazen and you will realize how full of unreal thoughts humans are. Such unnecessary useless thinking!’ (Talks on the Ten Ox-Herding Pictures)

Reading this again, it might sound a little harsh. Thoughts are real in themselves, but I would say that generally we spend too much time conjuring up scenarios that have no basis in reality and only serve to wear us down.