This refers to when two or more people encounter each other in completely coincidental fashion. You might notice your old classmate from three countries away is now your waiter in a place you had no reason to expect them in, and you might say "wow, what a small world". You might notice two people who you know from completely different spheres miraculously know each other. You might recognize by chance that your penpal has made a cameo at a venue you're at.
But what was your most profoundly coincidental encounter?
While doing groceries on the other side of the city I saw a friend from high school in front of the entrance. We said hello to each other and were just about to go our own way, as another friend from uni walks up to us and says hi. We all know each other, so I thought the two of them were meeting. But we all were thinging that about the others and after a short while we found out that none of us had made any plans of meeting. It was pure coincidence that we all three were there at the same time. Only happend once to me.