And what are the odds people meet in the first place? Those exact same factors are what make folks run into each other again later. It would actually be weird if you never ran into people you know.

>…Bangalore. Our trips had nothing to do with each other, other than we both work in tech and were visiting tech companies.

Bangalore is a tech city, and you both worked in tech. That's how you ran into each other.

Like the birthday paradox: If there are just 23 people in a room, then there's a 50% probability that two people share the same birthday.

And is this for day-month or day-month-year?

This for day-month.

I'll throw you another curve ball:

He was working in the same complex, and we'd run into each other at lunch.

The project he was there for was one I would have been assigned to, if I hadn't left our previous company. (I was the #1 SME for that bit of software)

Therefore, I would have been the one sent there anyways that week, and been in that area. I actually confirmed this with my old boss.

I'm surprised at how few times I've run into people I know when out and about shopping or doing other normal daily activities.

I live and work in a town with a population of around 11k. Coworkers live in that town, or one about 9 miles away with a population of around 22k, or one with a population of about 41k that is about 20 miles away in the same direction as that second town so the second town is in the middle.

This area has one Best Buy, one Target, one Barnes and Noble, one Walmart Supercenter, one Office Max, one Staples, and one mall all located in the middle town except the Walmart Supercenter which is in the 11k town. There are a few movie theaters but the quality varies a lot and most people I know only go to 2 of them.

In ~20 years these are the only times I've run into people I know which out doing ordinary things:

1. Two times I ran into a coworkers or former coworker at Best Buy.

2. One time at a gas station I saw a coworker getting gas at the same time.

3. One time I ran into a coworker while grocery shopping.

4. One time I ran into my dental hygienist while grocery shopping.

5. One time my doctor was having lunch at the same sandwich shop as me.

I would have thought that in 20 years, with a pool of 2 or 3 dozen coworkers or former coworkers living in the area, I'd run into people I know a lot more often.

This is because the group of people who travel often is surprisingly small, and so overlap will happen much more likely than you think.

> how often people who know each other randomly run into each other in an airport.

> I mean, what are the odds?

This is explicitly stating "any two people" (and it's at an airport not a plane, so more people). But then follows up with changing the framing of question they're asking:

> I only had it happen once, but it was nuts.

The birthday paradox is only a paradox because we tend to think of birthdays in a very personal manner. So when we think of "any two people sharing a birthday" we immediately change this to "someone having my birthday", without realizing we've fundamentally changes the question we're asking.

I was in two classes where the birthday paradox was discussed, at different universities. Both times it was my birthday that was shared with someone else. What are the odds?

Have had a handful of similar scenarios, seeing someone I know when we are in a far-away random place. I think it had to do a lot with I was traveling frequently at the time (200K miles/year), to all kinds of random places.

But I know 200 people, and I take ten flights a year, there are about 200 travellers on each flight, and such random bumpings don't happen more than once a decade. It's rather unlikely that I won't randomly bump into someone I know, on some flight, sooner or later.

But when it does happen, I'll still be surprised.