The Baader–Meinhof phenomenon is named after a German terrorist group active in the 1970s.
A Minnesota newspaper reader noticed the phenomenon in 1994: one day he was talking with a friend about the group. The next day, he encountered an article in the newspaper mentioning the group, although there was no special reason to expect it would be in the news.
The reader wrote a letter to the newspaper sharing how he became aware of the terrorist group and then read about it soon afterward. This sparked a discussion among other readers who had experienced the same phenomenon, leading to the coining of the term.