It’s hard to tell this story because it sort of breaks my heart. It was 1933, and my mother was five. She and her parents were driving along a country road at the eastern tip of Long Island, long before it was called The Hamptons. Suddenly traffic stopped, and cars began to line up and inch toward what they figured must have been an accident. They crawled along for a few miles, my grandfather running out of patience.

When they got to a fork in the road, they realized that a car had run out of gas just where the two lanes separated, and right there was a black man holding a gas can, his thumb in the air, hoping for a ride. My mother stood up in the back seat and watched car after car in front of them slowly go around the man.

“Stop and pick him up,” my grandmother told my grandfather, exasperated by the behavior of the drivers in front of them. I like this part of the story, of course — my grandmother so ahead of her time. But there’s another part.

As they got close to where the man stood, my grandmother glanced at the back seat next to where my mother was sitting. She took a newspaper from the floor by her feet and handed it to her small daughter.

“Spread this out on the seat next to you,” she told her.

“Why?” my mother wanted to know.

“Diseases.”

My mother did as she was told, and they stopped. The man, jubilant that this would end his humiliation, went to get in. My mother watched him closely. He saw the newspaper. His smile faded. He got in anyway. My mother remembered the sound his body made as he sat down on the paper designed to keep his “diseases” off their car seat. He took off his hat. He thanked them.

My mother told me that story when I was a young teenager, deep into my “Peter Paul and Mary Know the Answers to Everything” years. My reaction was harsh. How could my grandmother — my smart, kind grandmother — ever do such a thing? And why was my mother telling me this story with nothing more than a little frustration, saying, “Well, they did what they could do.” All I could see was that they were just another smack in the face to the black man who’d stood in the hot sun waiting for someone — anyone — to drive him to a gas station.

My mother told the story because all those years later, she still remembered the hurt look on the man’s face, and it haunted her. She told it because she also understood her parents’ actions in a way I refused to. Because the world evolves in fits and starts, brave take-offs and hard landings, good intentions and horrible blunders. She told me the story slowly and quietly because I thought I knew everything about the universe and how it worked. And she knew that wasn’t true.

And now I know it, too.