The faculty, staff, and student body at BPI often chatter about coincidences, and history offers plenty of coincidences. Like the story of Kevin Stephan, a Buffalo man who saved the life of a woman who had saved his life 9 years earlier. That’s too amazing to be mere coincidence, right? Well….

Actually it’s not all that amazing. While the probability of any single trained rescuer saving the life of someone who had previously saved his/her life is remote – on the order of one in millions – there are tens of millions of trained rescuers in the U.S. Even if you limit rescuer-rescuee pairs to those living in the same city, as Stephan and his rescuer-cum-rescuee did, that’s a whole lot of possible pairs.

A whole lot, as in … the probability of a story like Stephan’s happening somewhere in the U.S. in a given decade is about 1-in-3. No one thinks it astonishing that someone was born on a Monday – a 1-in-7 event – so why would a 1-in-3 event like Stephan’s amaze us? Yet on a TV show this week I heard explanations ranging from Jungian synchronicity to quantum entanglement.

It turns out we’re not very good at intuitively guessing how likely something is, or even at weighing known probabilities. Most poker players know a pair of Aces in the best starting hand in Texas Hold’Em, and that pocket Aces are about a 6:1 favorite to win over any other starting hand. Put another way, the probability that pocket Aces will lose to a random hand is the same as the probability of a person being born on a Monday: about 1-in-7.

Yet I can’t count how many times I’ve heard poker players use words like “unbelievable” after losing a hand with pocket Aces. I’ve even heard players claim cheating as the only explanation … which is like claiming the only explanations for being born on Monday are artificially induced labor or a scheduled Cesarean section.

Realworldia is a big place, and history is a long time. Lots of things happen, and there being only 365¼ days in an earth year, that means lots of things happened on any given date in history. Sometimes it’s not even mere coincidence. There were more recorded battles fought in late-spring and summer because that was the traditional military campaigning season: after crops were planted and before harvest time and the bad winter weather. Likewise for the founding of countries, a surprising number of which happened in late June and July.

I play with these coincidences for fun, but please don’t take them too seriously, nor think that I do. And be suspicious when someone says “That’s too amazing to be just a coincidence.” Coincidences happen … every day.