For years, I had retold a story from a time in Ghana when my brother and I were toddlers. As I recalled it, he had parked our old iron tricycle on a small cobra. The trike was too heavy for the snake, which remained trapped under the front wheel. 

But after my aunt and my mother had both passed away, we discovered a long-lost letter from Mom recounting the incident. In reality, I had parked the tricycle on the snake, and my brother had run to tell Mom. Her eyewitness account, written close to the actual event, revealed the reality.

The historian Luke…