The Baader-Meinhof Phenomenon happens when you learn an obscure fact or trivia, and soon thereafter you see another reference to that new thing. This is similar to the frequency illusion which is defined

Over the last few months I have been posting less frequently on Steemit as other things have prioritised themselves. I was walking through some countryside and noticed what I thought was a Steem symbol.

The Baader Meinhof phenomenon (or the frequency illusion as it's also known) is one we are all familiar with even if you've never heard of it before. If you haven't, be prepared to hear about it again