If you go back in time and change things, will the world end in disaster?

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I'm an avid science fiction fan, and I've seen about every time travel movie there is. I've always believed that if you go back in the past and change things you will mess up the future or maybe even the whole planet. But, in two representations of this dilemma that I've seen recently this is not the case. In the Time Travelers Wife, Henry the time traveler, can't actually change anything so therefore cannot disrupt the universe. In the second case, with the movie Before You Say I Do, everything works out even better for the characters because of the change that was made. What do you think? If you went back, would you try to change stuff? Or would you be too afraid to mess up the world? I think that depending on the severity of the situation I might try to change things but as I said I believe that you might have unintended consequences. It'd be a hard choice.