To paraphrase Mark Twain, accidents can sometimes turn out to be the greatest inventors of them all. Not every error leads to disastrous consequences. Sometimes, when we get things wrong, a situation can turn out even better than we'd ever imagined. These are the best kinds of mistakes. Instead of leading to misfortune, they give us something wonderful and totally unexpected.
If a petri dish hadn't been left open in Alexander Fleming's laboratory, for example, the world might have had to wait many years for the invention of penicillin, and that's just one example of many amazing things throughout history which came about purely by accident. This even applies to the world of Hollywood. Some of the most successful movies and iconic scenes might never have existed without a few 'happy little accidents' along the way.
Movie-making is normally a pretty strict business, with countless workers and executives painstakingly perfecting each shot and line of dialogue, but unexpected accidents happen on every set. Often, they don't lead to anything good, but they can sometimes actually make the movie even better than it was before.