A courtroom drama I watched recently on TV illustrated how faulty our memories can be. In the storyline, a man was on trial for murdering a shopkeeper, and the shopkeeper’s wife was the star witness. Although robber was wearing a mask and a ball cap, she identified the defendant as the man she witnessed shooting her husband.

Through investigation, it was learned the defendant had visited the store the previous day and talked to the woman. He decided prices were too expensive for him and left. That’s why she recognized him.

Some of my memories are like snapshots. I can see people and places in...