It's a concept in Chaos theory in which

small things can have non-linear impacts on a complex system.

Nearly 45 years ago, during a meeting of the American Association for the Advancement of Science(AAAS), MIT meterology prof. Edward Lorenz asked a question: “Does the flap of a butterfly’s wings in Brazil set off a tornado in Texas?”

Ever since then, it became all most a cliche in popular culture to refer to small things that cause out of proportion significances. Most famously used in the once best seller book" Freakonomics: A Rogue Economist Explores the Hidden Side of Everything" By Steven Levitt.  https://www.goodreads.com/book/show/1202.Freakonomics