Coca-Cola surprised fans and rivals alike in April 1985 when it replaced its original soft drink formula. The company had conducted extensive taste tests of so-called New Coke before making the switch, but many consumers felt betrayed, and they expressed their outrage in more than 400,000 calls and letters.

Less than three months later, the company brought back the original Coke as Coca-Cola Classic.

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After the dust settled, what BusinessWeek magazine called "the marketing blunder of the decade" actually worked out well for Coca-Cola, boosting its overall sales and revitalizing interest in its flagship brand. That led some to speculate that the company had planned it that way all along, a charge then-President and CEO Donald Keough denied.

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"We're not that dumb, and we're not that smart," Keough said at the time.

Continued: Lather; rinse; repeat