One example I could think of is “When Fans are more excited for a cameo character rather than the main character “
She Hulk, Book Of Boba Fett, and Even Black Adam are examples of this. Fans should be more excited about the main character, not the cameo, if you write the main character in a way that makes them bland or unlikeable, that’s a sign that the story and the whole project won’t work at all.