Also known as 'the Baader-Meinhof phenomenon', 'Diegogarcity', or
'Plate o' Shrimp', it's one of the little weirdnesses
of life and of cognitive function.
You learn about or hear of something seemingly obscure for the first time, and you go, "Huh."
Then, within the next few days, you encounter it again in another
context, maybe even multiple times. This time, you go, "Huh. Weird."
It's everywhere all of a sudden. What? What's going on here?
The phenomenon is cited, along with deja-vu (and its
brothers, jamais- and presque-) and
synchronicity, as an example of: apophenia and the
recency effect, memetics and the Zeitgeist, or of
Jung's collective unconscious, depending
on who exactly it is you're asking.
The apophenia/recency explanation is the most widely accepted and explains the perception like this: when you encountered the idea initially, and it clicked for the first time in a memorable way, your brain kept it there in reserve for a couple of days before it would have gone the way of all accumulated knowledge. Within those couple of days, you, purely through coincidence and your heightened awareness of the idea, encountered it again and because it was so recent, you really noticed. By this time your brain is primed and on the lookout for anything having to do with that word and so, if it is at all possible, you will again. Your brain filters out all kinds of repeated stimuli; this was just the one you happened to notice.
The memetics explanation is similarly concrete, but posits that you are noticing the trigger because a concurrence of events have conspired to bring it more into the public eye, like the use of a phrase on a billboard or in a popular television show or recent bestseller, and that people unconsciously repeat it and it builds exponentially from there.
And according to the idea of the collective unconscious, you've noticed a symptom of the way we are all connected and draw from a shared body of unconscious knowledge and experience. In a similar school of thought, maybe this is a 'sign'. It's worth noting that while this type of explanation, rhetorically, seems the most farfetched, memetics can also be classified as pseudoscientific and apophenia is theoretical.
This phenomenon might be called reticular activation when
experienced visually, and is also somewhat related to the Discordian
Law of Fives.
A man named Terry Mullen claims to have coined the term in a St. Paul newspaper two decades ago, after the German guerrilla group, over which he experienced the
phenomenon. Diegogarcity was similarly coined in a newspaper. Plate o'
Shrimp is from Repo Man and in the film itself arguably refers to
synchronicity in general. People occasionally bring it up in the
pop-culture press because it's so damn interesting (coincidentally,
Damn Interesting has what may be the definitive article on the
phenomenon) and moreso since the 2008 release of an unrelated film, the
Baader Meinhof Complex.
I believe that there might be a set of common characteristics
that make some words or concepts stickier than others. /msg me with
your Baader-Meinhof moments and let's find out.