A couple of years ago, in the gym, I mistakenly greeted some guy, mistaking him for someone I knew. I realized my mistake instantly, but there was no turning back. Since then, we've been regularly greeting each other, like people who have been through thick and thin together. We've never actually talked; I don't know who he is, what his name is, or why he's always in the same place as me, but our silent greetings last longer than many meaningful acquaintances.