The fault with the movies, dear reader, is not with the stars, or even with the studios, but with ourselves. From Mark Harris' “Five Came Back: A Story of Hollywood and the Second World War”:

The weekend of Pearl Harbor, [director George] Stevens was coming off a disappointing test screening of Woman of the Year. His producer at MGM, Joseph L. Mankiewicz, had told him that audiences had rejected the movie’s last scene, in which Hepburn and Tracy reconciled while covering a prizefight. They wanted to see Hepburn brought low, humiliated for her careerism. Reluctantly, he was preparing to shoot a new ending, in which Tess was to be shamed by her inability to find her way around a kitchen and cook a simple breakfast.

Hepburn supposedly hated the new ending, and from today's perspective it certainly seems odd. 

What else have test screenings and market research got wrong? A lot. (See “market research” tag below.) They forced a new ending on the otherwise beautiful “Magnificent Ambersons.” They were against Clint Eastwood teaming with an orangutan, as well as most everything about “Pulp Fiction.” They gave low ratings to, among other TV shows, “All in the Family,” “The Mary Tyler Moore Show,” “Seinfeld” and both the UK and US versions of “The Office” Basically, if it was new they were agin it. Which is why, if you want to make a mark, you never listen to market research. You listen to your gut. And by “you” I mean “me.”

Brought low. Shamed.