Courtesy of Curiosity.com:
“You’ve probably heard that a butterfly can flap its wings in Brazil and set off a tornado in Texas. This is known as the butterfly effect, and while it shows up in everything from metaphors for human connection to the behavior of the stock market (not to mention an arguably low point in Ashton Kutcher’s career), it got its start with a mild-mannered meteorology professor named Edward Lorenz. Just by rounding a few decimal points, he changed science forever.
One day in 1961, Lorenz was working in his office at MIT, entering data into a newfangled computer program designed to simulate weather patterns. The simulation was a repeat of one he’d run already, but this time he rounded off one of his 12 variables from .506127 to .506. Then he left his office to grab some coffee while the computer crunched the numbers.