I'm sure it has happened to you and if it hasn't perhaps you just haven't noticed. In any case, I found this phenomenon has a name. It's called The Baader-Meinhof Phenomenon, also more commonly known as Frequency illusion.
It is a cognitive phenomenon where you think that after you learn about something you see it more often. The fact is that most likely that thing, whatever that may be has been there all along. But our brain works by analyzing and noticing patterns so after you learn about a pattern which could really be just a new word or the type of a widget or building or a thing, then your brain starts noticing it more often. That's just how that works.
You may actually experience the Baader-Meinhof Phenomenon by finding the Baader-Meinhof Phenomenon mentioned in the next few days or weeks. Pay attention. That would be a stretch, but it isn't that far fetched. That is exactly how it happens. I've been noticing this since I was young, but never thought that I could explain it. I never thought it even had a name.
Part of the phenomenon is that when you find a new word, new pattern or a new thing as I mentioned above, you will likely notice a recurrence of this new experience in the near future. Maybe a day or a few days. Try it out, go read some wikipedia articles and learn something new. Read a newspaper or magazine that you don't normally read, watch a show outside of your favorites. It may just trigger the Baader-Meinhof Phenomenon.
So there you have it, one interesting tidbit for you today. I found the name for this by watching a random video the other day. I don't even know how I found that video, but you may like it too. It's chock-full of really cool terms you never knew existed. It's titled: Everyday Things You Never Knew Had Names.