I seem to be gravitating towards the idea of something being in two places at once. Through looking at the idea of quantum superposition, quantum entanglement and consequently the idea of parallel worlds and time travel, I've found the concept that something can be in two places at once and even interact with their other self perhaps without even knowing really interesting.
Although this is a really lame example, it's the best one I can think of to explain the point:
In Harry Potter and the Prisoner of Azkaban, when Hermione tells Harry and Ron that she has been using time travel to get to all her classes, and then uses this time travel to take them back to before the griffin creature...thing...is killed. The first time round before they travel back in time, they are in Hagrid's hut and are warned to leave by somebody throwing a large seed through the window. When Hermione and Harry go back in time, they get worried as the seeds have not been thrown and their past selves need to leave. It is then that Hermione realises that it was their future selves who threw the seeds in the first place.
This is a really clever video that somebody made and posted on YouTube. They've split screened the first time round Harry, Hermione and Ron go to Hagrid's House on the left, and then on the right hand side is what's happening at the same time when Hermione and Harry go back in time.