Yet another mental phenomenon can be used advantageously by comedy writers: audiences tend to fill in any gaps. Our minds continue an image on to its natural conclusion and supply anything that might be missing. It’s this peculiarity that makes stage magic work. Magicians show an audience only so much— the audience assumes the rest. The key to the trick is generally where that assumption is made. People say, “I know he put the coin in his right hand. I saw it there.” They really didn’t; they just assumed it should be there and so their minds told them they “saw” it there.
– Gene Perret, How to Write and Sell Your Sense of Humor (1982)