I'm watching a movie which involves time travel and I have a question. I realize that Hollywood is clueless when it comes to a great many things, but this piqued my interest. A man named Rufus is stating that, in his time, "things are great, but they almost weren't". Now Rufus is required to go back 700 years into the past to remedy a situation that would negatively affect his time. Given that Rufus is enjoying great things in his present time, why would he be required to travel back 700 years to remedy a situation? The fact that Rufus is enjoying great things is proof that the issue 700 years ago was already resolved (cause and effect), otherwise Rufust wouldn't be enjoying great things. If his present timeline is the result of previous alteration, why is he required to perform the work again? I believe I have a basic understanding of temporal mechanics, but I find this type of thing very interesting and I would like to learn more.