Genres are slices of a whole life view. Life can be romantic, hilarious or haunting at times, but individual lives are not all these things at once. To make it easy for storytellers to communicate with their audiences, storytellers tell you stories using a small selection of human emotions, conditions, and details that reflect qualities we see when we’re feeling especially romantic, humored, frightened, etc.
So a movie like You’ve Got Mail we understand to be a romance (this movie is also known as a “chick-flick” by some, but I think it is above that). You’ve Got Mail doesn’t suggest that all life experiences reflect the romantic, comical, and dramatic emotions we see in this movie—just that the story in the movie happens to show only those bits and pieces (of a bigger story) that reflect romantic, dramatic, and comical events in life.
A genre is like one piece of a big all genres pie of life. The pie has all genres as part of it, but any given movie/novel/story is only one slice of the genres pie. (Sometimes genres are mixed together for a story, and I will address these more complex stories soon.) So any given movie should not be criticized that “life is not like that” because it is at times—just not all the time (this exempts audacious story content that is beyond the realm of plausibility).
Genres help us to understand human emotions better and situations that we have not personally experienced. While they are helpful in the abstract to help us reach a proper interpretation of fiction, they are not the only clues that express to readers/audiences a story’s intended meaning.