Many years ago, during one of my summer visits to my family in Brazil, I went to visit my ailing, housebound grandmother. I took the bus to her neighborhood and walked from the bus stop to her apartment building. Way down the block I spotted my father, walking toward me.

Dad wasn’t very tall—about 5-foot-4, I’d say. His large skull was totally bald on top and scraggly on the sides. On this occasion was dressed in the garb he wore daily to his job teaching at the university hospital: grey trousers, white shirt, brown cardigan. His walk was endearing, somewhat ridiculous, and absolutely individual. He took fast, small steps, always looking down at his feet, lost to his inner world, thinking and thinking—that was his thing, thinking.

As he walked toward me, he ate popcorn out of a paper bag. In Brazil you can buy fresh popcorn from street carts, much as you can buy pretzels in New York or crêpes in Paris. I come from a family of popcorn fanatics. We eat a lot of it, we eat it often, and we eat it in public as well as in private.

Dad was so absorbed in his popcorn and his inner world that he didn’t see me walking toward him. I decided to play a joke on him. We got nearer and nearer to each other, and right when he were side by side I put my mouth practically in his ear and asked, “You enjoying your popcorn?”

Dad was totally freaked out, of course. He looked up at me with alarm in his eyes. It’s not every day that a total stranger invades your inner world for no good reason.

For a microsecond I was proud of my joke. Then it was my turn to freak out. The guy wasn’t my father at all! He happened to look like my father, dress like my father, walk like my father, and eat popcorn like my father. And he happened to be at my grandmother’s neighborhood, as my father was likely to be two or three times a week. But—he wasn’t my father.

I have no idea who that guy was or how he reacted to my assault, because I didn’t hang around to find out. When I realized I had made a mistake, I sped away without looking back. I rushed to grandma’s and sat at her feet for an hour, pretending that I was the angel she had long thought I was. Why spoil her illusions? That’d have been quite selfish of me.

The moral of the story is, “You can’t ever be totally sure of anything. It doesn’t matter how much evidence you have in your favor, you still risk being wrong. Everyone in this world has been wrong and will continue to be wrong from time to time, or often, or even always. DO NOT COUNT ON YOUR PERCEPTIONS AND SUPPOSITIONS ALONE TO NAVIGATE THE WORLD! USE YOUR DISCERNMENT TOO! AND THINK TWICE BEFORE PLAYING A JOKE ON YOUR FATHER!”