Artistic Serendipity - your fave

In this thread I mention that Black Sabbath’s sound evolved fortuitously because Tommy Iommi lost a couple of the tips of his fretting fingers in a manufacturing accident. He therefore detuned his guitar so it hurt less to fret strings. The change in guitar tone changed how they sounded and led to a different approach to songwriting, etc…

What are some of your favorite “happy accidents” in art? Editing “Jaws” to avoid showing the phony-looking shark, which led to a much more mysterious and ominous feel for the film?