Goldilocks effect
n. When something succeeds or prospers because it is neither too big nor too small.
Size does matter. Up to a certain point, the more widgets you produce, the cheaper each widget becomes. But you no longer have to be General Motors to reap economies of scale. Several recent studies suggest a Goldilocks effect: medium-sized companies enjoy the benefits of scale more than the big ones do.
—James Surowiecki, “The Goldilocks effect,” The New Yorker, May 27, 2002
1987 (earliest)
The new funding rules are creating a "Goldilocks effect," explained Henry Savath, vice president at A. Foster Higgins Co., the employee benefit unit of Johnson & Higgins, New York. "It can't be too great, it can't be too little, it has to be just right."
—Nicky Robertshaw & Joel Chernoff, “Budget details pummel funds,” Pensions & Investment Age, December 28, 1987