Instead of acting myself, I continued to silently single out other people on the train — mothers, a businessman, a group of women my age. I made pointed eye contact with them, silently urging them to act. But I did nothing, even as I saw the man crouch down, examining the flimsy metal divide keeping him on the safe side of certain injury or death.

And then, after a terrifying moment where I thought he had already gone, I saw the man straighten and pass into the next car.

I was left trembling, disturbed by what I’d seen but also afraid of what I had learned about myself. I realized I was what psychologists call a “bystander” — a person who, upon seeing someone in trouble, does not intervene under the assumption that someone else will.