Which famous product failure accidentally led to the discovery of the adhesive eventually used in Post-it Notes?

Some of history's most famous invention failures led to unexpected discoveries or taught valuable lessons that shaped future innovation. Behind many successful products we use today are fascinating stories of initial failures, pivots, and unexpected applications. This trivia tests your knowledge of how certain product development failures ultimately contributed to significant discoveries or innovations in unexpected ways.

This is a live public trivia poll on AIPolls.Net. Vote and see real-time results.

Spencer Silver's failed super-strong adhesive at 3M that was deemed 'too weak' for industrial applications
Pfizer's unsuccessful hypertension medication that was repurposed after unexpected side effects during clinical trials
Coca-Cola's New Coke formula that was quickly abandoned but provided valuable consumer insights
Sony's Betamax video format that failed commercially but advanced recording technology