In 1991 my GF vetoed a suggestion by me that we go to see Pearl Jam at a small local club. This was 2 years before they became my totally favourite band of the moment and 3 years before they became mega-famous stadium material. A missed opportunity that I cursed for a decade afterwards.
In 1993, just after crossing the Golden-gate bridge on a bicycle and shacking up in some grotty backpackers, I was invited by some fellow backpackers to go and see The Grateful Dead who were making an apparently very rare live appearance that very evening somewhere in some groovy part of San Francisco. I declined the backpacker invitation and the legendary Grateful Dead went on to split up 2 years later to end a revered 30 year career. I did not end up lamenting this decision though, since I was never a fan of the band and I have thought for a long time that all hippies should be burned.