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“”A lot of people don't realize what's really going on. They view life as a bunch of unconnected incidents and things. They don't realize that there's this, like, lattice of coincidence that lays on top of everything. Give you an example, show you what I mean: suppose you're thinkin' about a plate of shrimp. Suddenly someone'll say, like, "plate," or "shrimp," or "plate of shrimp" out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconsciousness.
|—Miller in the film Repo Man (1984)|
The frequency illusion (also known as the Baader-Meinhof phenomenon) is the phenomenon in which people who just learn or notice something start seeing it everywhere. For instance, a person who just saw a movie about sharks might start seeing the word "shark" everywhere. This is not necessarily because the person really has come across more instances of the word "shark"; rather, before seeing the movie, they usually simply passed the word over and quickly forgot it, while later, after having seen the movie, the word started sticking in their memory.
Research into the perception of low probability events suggests that frequency illusions come from a combination of imaginability and the manner in which data is presented. If a rare event is presented as having a 1 in 1,000 chance of happening, that event will seem more likely than if presented as 0.1% chance of happening. Using integers to show the chances makes it easier for a person to imagine themselves facing the unusual event. Add in a little danger (would seeing the word "ant" have the same effect as "shark"?) and, voilà, frequency illusion.