From Chapter 19 ("You Can't Get Off the Train") of No Beginning, No End: The Intimate Heart of Zen by Jakusho Kwong:

... I think it's pretty true to say that we're all on a train. The scenery is going by quickly, and you can't hold on to anything; you have to stay and keep going down the track. It's when you hold on to something, or even try to hold on, that you are not on the train anymore. But our way tells us to release what we are holding so that we can keep going and stay on track. What it really comes down to is the wisdom and compassion of non-avoidance. You just keep going, and as you do, working with the practice called the compassion breath, you know how to transmute what you see, hear, smell, taste, touch, and think every day. And the truth is that, with practice, this process helps you learn to be kind to yourself and to all beings as well.

We have the capacity to take in an enormous amount of negativity and to let it go its way. We don't avoid anything because we know we can work with it. Most people don't know what to do when they notice unwanted thoughts and feelings within themselves, or see a dead animal on the road, or killing on television shows or in the news, or the many homeless and starving people right beside them as they walk down the street. And then there's drugs, alcohol, AIDS, and cancer. People feel overwhelmed, and the result is that often their hearts turn hard and cold. I'm sorry to say it, but it's true. The normal response to these things would be that everyone should be crying—this is the awakening of compassion—but the ignorance of sentient beings causes us to continue to enhance samsara. The practice of compassion breath allows our hearts to remain soft and open while our spirit and life-force are replenished. And our tears are part of this replenishment, an important part. You do not have to be a Buddhist to do this; it is meant to be used by all human beings, everywhere, even while standing on a train. ...

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