Which packaging innovation was initially rejected by consumers but later became ubiquitous after a marketing campaign rebranded it from a 'pouring problem' to a convenience feature?

In the world of retail, packaging design isn't just about aesthetics—it's about innovation that solves real problems. Throughout history, certain packaging breakthroughs have revolutionized entire industries, creating new markets and changing consumer behavior. This trivia question focuses on a groundbreaking packaging innovation that transformed product accessibility and convenience, creating a billion-dollar industry shift in the process.

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The resealable cereal box (Kellogg's 'Pour & Store' design)
The upside-down ketchup bottle (Heinz's 'Easy Out' design)
The pop-top soda can (Reynolds Metals' 'Pull-Tab')
The stand-up toothpaste tube (Colgate's 'Ready Stand' design)