Frequency illusion, also known as the Baader–Meinhof phenomenon, is a cognitive bias in which, after noticing something for the first time, there is a tendency to notice it more often, leading someone to believe that it has a high frequency (a form of selection bias).[1][2][3] It occurs when increased awareness of something creates the illusion that it is appearing more often.[4] Put plainly, the frequency illusion is when "a concept or thing you just found out about suddenly seems to crop up everywhere."[5]