This is that effect of suddenly noticing things we didn’t notice that much before — but we wrongly assume that the frequency has increased. A perfect example is what happens after we buy a new car and we inexplicably start to see the same car virtually everywhere. A similar effect happens to pregnant women who suddenly notice a lot of other pregnant women around them. Or it could be a unique number or song.
It’s not that these things are appearing more frequently, it’s that we’ve (for whatever reason) selected the item in our mind, and in turn, are noticing it more often. Trouble is, most people don’t recognize this as a selectional bias, and actually believe these items or events are happening with increased frequency — which can be a very disconcerting feeling. It’s also a cognitive bias that contributes to the feeling that the appearance of certain things or events couldn’t possibly be a coincidence (even though it is).