‘It ain’t over till the fat lady sings’
This phrase evokes the image of the stereotypically fat soprano that closes out an opera show, specifically “Götterdämmerung,” the last of Richard Wagner’s “Der Ring des Nibelungen” cycle of operas.
At the end of the show, the Valkyrie Brünnhilde — usually played by a big woman — has a 20-minute farewell scene right before the finale of the entire opera cycle.
“It ain’t over till the fat lady sings” is usually meant to be encouraging, a reminder that the present circumstances do not necessarily indicate the outcome of a situation, particularly when it comes to games or sports.