It was 30 years ago today that Coca-Cola announced its decision to change the formula of its 99-year-old flagship beverage. As the company notes on its corporate blog, "mayhem ensued." More than 1,000 calls flooded the company's consumer hotline per day. Many consumers wrote passionate -- and sometimes profanity-laced -- letters to the company. The Coca-Cola archivists scanned and posted their favorites online.

The New Coke debacle became a cautionary tale for marketers everywhere. As part of a package noting the company's 125th anniversary in 2011, Ad Age interviewed Sergio Zyman, the charismatic former chief marketer of Coca-Cola, and Marcio Moreira, part of the group of McCann execs that worked on the product's launch.

"I think we were lazy in really recognizing that we needed to reactivate or reposition the brand. If we had done that through an advertising process, I don't think New Coke would have ever happened, but there was such resistance to any kind of change in the advertising position of the brand that we introduced a change in the taste," Mr. Zyman said. "I know, you'll say that 's ridiculous, and I agree. But it happened."