When people watch a movie, they not only expect a good story, but also a lot of conflict. Because every fictional work, visual or written, needs problems and obstacles, many audiences expect satisfying endings, where the protagonists achieve their goals. If they don’t, then it’s either because they realized those goals weren’t what they wanted all along or they weren’t the right kinds.
Twenty-three days have passed since Thanos wiped out the world’s population. The remaining Avengers get together to figure out how to fix the problem. The final idea is to go back in time to stop Thanos from succeeding.