The Baader-Meinhof effect is experienced when someone learns about something new, then begins seeing that new thing everywhere. The term is named for a German terrorist group from the 1970s. According to Psychology Today, a guy named Terry Mullen learned about the Baader-Meinhof group one day, and saw its name pop up again the next day, having gone his whole life unaware of the militant ultra-left organization. He wrote about the phenomenon in a letter to his local newspaper, and the Baader-Meinhof effect was named.
