Setups and Payoffs

What are set-ups and pay-offs?  Why are they so important in the screenplay you are writing?

    Set-ups and pay-offs are ways for the story to logically develop, creating a sense of inevitability and cohesion that make the resolution feel more earned. Essentially, set-ups are where you establish a line of information which will be relevant and/or affect the story later on and pay-off are where that information or detail comes back and accomplishes something. These are so important in writing a screenplay because they help the story flow better and the important details feel like they are earned and fit; it breaks the audience's suspension of disbelief when a new piece of the plot appears with no set-up. Additionally, having this system in-place can improve the audience's engagement and keep them interested with more info-heavy stories.