It ain't over till the fat lady sings

"It ain't over 'til (or until) the fat lady sings" is a colloquialism which is often used as a proverb. It means that one should not presume to know the outcome of an event which is still in progress. More specifically, the phrase is used when a situation is (or appears to be) nearing its conclusion. It cautions against assuming that the current state of an event is irreversible and clearly determines how or when the event will end. The phrase is most commonly used in association with organized competitions, particularly sports.

The proverb is used in baseball circles, such as "the Texas Rangers didn't hear a fat lady sing" when the Rangers went down 2-3 in a seven game series against the Houston Astros.