[fan]

The transition is never that stark.

Take your example of sunglasses. A quick search on wikipedia shows that the precursor were glasses with a thin slit in them. It was never squinting, and then BOOM, Oakleys.

There was always a gradual change that is only missed in retrospect because of how standardized and popular the winner is.

Name a few popular products and services, and I bet there have been similar solutions beforehand.