it's not over till the fat lady sings

The phrase "it’s not over till the fat lady sings" is an idiomatic expression used to emphasize that a certain event or situation is not yet finished or concluded, and one should not assume the outcome until the very end. It suggests that just because things may appear settled or one outcome seems likely, there is still a possibility for unforeseen circumstances or a twist that can change the final outcome. The phrase is often associated with opera where a large, operatic soprano singer typically performs at the end of the production, but it has been extended to various contexts beyond the world of opera.