For Want of a Nail.

This trope can also be referred to as the butterfly effect, where one small change can ripple through time, changing everything. This idea is heavily explored in the film The Butterfly Effect, where Ashton Kutcher's character is able to revisit events in his childhood and change what happened to change the present, each possibility being extremely different from the last.

Occurrences in The Butterfly Effect also carry across into Bioshock Infinite, such as when the brain remembers new memories which should never have been in your head, the brain hemorrhages, causing a nose bleed.

The Simpsons has also played on this idea in a Treehouse of Horror episode where Homer fixes a toaster, accidentally creating a time machine, where tiny, insignificant events such as stepping on a plant end up irreversibly changing the present in crazy ways, as is style for The Simpsons.

Blackadder also covered this topic in a christmas special, with Rowan Atkinson changing the present in numerous ways, such as causing the British to become French, and causing Shakespeare never to write, but is credited with the invention of the ballpoint pen. He and Baldric then go back through time, fixing their mistakes, however, Blackadder himself fixes it so his descendants rule Britain.

The film Back to the Future is yet another prime example of this, where Marty McFly  travels back in time and changes his father's past to make him a more confident and successful man, changing the present so that his father's boss becomes his father's car cleaner.