Clustering illusion
The clustering illusion is the tendency to see meaningful clumps or streaks in data that are actually random. True randomness often contains runs and bunches, so we mistake them for signs of a hidden cause.
In everyday life
A shuffled playlist plays three songs by the same artist in a row, and the listener decides the shuffle feature must be broken.
Looking at a map of house fires in your town, you notice four on one street last year and decide something about that street must be causing them, though the rest were scattered all over.
Why your mind does this
Our ancestors survived by spotting patterns fast: rustling grass might mean a predator, and dark clouds meant rain. Filling gaps with a plausible story lets us act on thin information instead of freezing. A brain that sometimes sees a pattern that isn't there loses less than one that misses a real threat.
Its family, in 30 seconds: Stories & patterns
How to spot it
Ask whether a purely random process could easily produce the bunching you are seeing.
How to counter it
Compare the pattern with a random version, such as a row of coin flips or shuffled data, to see if it really looks different.
Same family: Stories & patterns
SourcesFalk & Konold (1997)·Wikipedia