MY sisters and I have often marveled that the stories we tell over and over about our childhood tend to focus on what went wrong. We talk about the time my older sister got her finger crushed by a train door on a trip in Scandinavia. We recount the time we almost missed the plane to Israel because my younger sister lost her stuffed animal in the airport terminal.

Since, fortunately, we’ve had many more pleasant experiences than unhappy ones, I assumed that we were unusual in zeroing in on our negative experiences. But it turns out we’re typical.

“This is a general tendency for everyone,” said Clifford Nass, a professor of communication at Stanford University. “Some people do have a more positive outlook, but almost everyone remembers negative things more strongly and in more detail.”

There are physiological as well as psychological reasons for this.

“The brain handles positive and negative information in different hemispheres,” said Professor Nass, who co-authored “The Man Who Lied to His Laptop: What Machines Teach Us About Human Relationships” (Penguin 2010). Negative emotions generally involve more thinking, and the information is processed more thoroughly than positive ones, he said. Thus, we tend to ruminate more about unpleasant events — and use stronger words to describe them — than happy ones.