Through Applied Phlebotinum, Functional Magic, or some other means, our heroes travel back to the past. In the past, they wind up being responsible for the very events that underpin their own "present." This creates a chicken-and-egg scenario, in which the looping sequence of events has no clear beginning. The result of breaking the zeroth law of Time Travel: do not cause the event you went back to prevent. For further discussion of this trope, see Wikipedia. Importantly, this trope is not to be confused with Groundhog Day Loop. Examples of Stable Time Loop include: