We need things to wrap up. We need natural, organic, comfortable ending points. Writing is about creating tension, then releasing tension. You absolutely cannot leave tension unresolved.
Well, actually, you totally can do exactly that. Creating tension and leaving it there can be a great way to make people uncomfortable. In the worst case, people simply tell you that you are a bad writer. But in the best case, it can unnerve people more than any actual horror novel.
Like the story of the girl in her basement. It's her little hang out spot. After school, she puts on some music, does her homework, chats online with her friends. Today, she finishes her last assignment, then closes her book. She coughs. Her book now has blood spots on it. She coughs again, this time into her hand, and finds thick, dark chunks mixed in with more blood. She gets out of her chair, confused what is going on. She violently hunches forward, vomiting a solid stream of blood. She becomes woozy, and starts swaying around the basement, her vision blurring, going gray.
When you leave tension unresolved, the reader wants more. They want a conclusion. Whether good or bad, they just need it to end. By ignoring it, moving on, or just cutting it short, you force the reader to accept that there is no ending, or at least that it is one you will not get to see. It may piss them off. Again, they could call you a bad writer. But they also may accept it as the kind of thing that happens in life and that they will just have to learn to accept it and hope that they can shake that nagging feeling at some point.