It was once wonderfully illustrated in an episode of King of the Hill. In an early scene, Khan, Boomhauer, and Bill are standing side by side in the alley on a blustery day. Khan is wearing a big cowboy hat. A gust of wind comes along, plucks the cowboy hat from Khan's head, gives it a single twirl over Boomhauer's head, and drops it square atop Bill's head.
The men are amazed! They decide that they have to videotape it for YouTube so that they can become internet stars. What follows is a long series of attempts to recreate the event, to no avail.
It's funny because we all know that the hat blowing off Khan's head and onto Bill's is just a fluke. It will never happen again. And that is exactly what "regression to the mean" means. It means, to coin a phrase, that "sh*t happens." But most of it never happens twice.
The "mean" is what we think of as "normal." And "regression" means "returning to." So the phrase literally means, returning to normal. Weird stuff happens, but then everything returns to normal.
This is part of life in a chaotic system, which our reality most certainly is. In fact, our reality is a lot "noisier" than we might think. There are flukes happening all around us, constantly, never to be reproduced. We don't notice many of them. Some are so astounding that we can't help but notice. And this is where we often get into trouble.
It is a huge mistake to confuse a fluke with a real phenomenon. Hats do not blow off one person's head and onto another's, except once in a million billion times. This is what we mean by "it's just coincidence," but it's easy to ascribe more meaning to "coincidence" than it really deserves.
Each of us can rattle off a list of bizarre coincidences. Just last month I woke up with a particularly odd phrase running through my mind ("You don't have to go home, but you can't stay here"). I shook it off, went downstairs, fixed my morning coffee, and turned on the TV to watch a rerun of last night's episode of The Daily Show. The first words out of Jon Stewart's mouth were "You don't have to go home, but you can't stay here."
This doesn't mean that Jon Stewart has a line directly to my subconscious. Nor does it mean that we are paired together in some strange Fate. Or that it was confirmation of coded instructions being beamed into my mind. It was just a fluke. It will never happen again - which is to say, it will regress to the mean.
But it's easy to see how someone else might not dismiss the experience so quickly.
The lesson here being to remember that life is chaotic, and weird stuff happens. Sometimes it's a fluke, and sometimes it isn't, and it's important to understand the difference.
Photo credit: Flickr/elkit