Chuck Amuck: The Life and Times Of An Animated Cartoonist gives a set of rules that more-or-less govern the universe of Chuck Jones's Road Runner cartoons. This list strikes me as a rich source of insight into the workings of creativity and comedy --
"1. Road Runner cannot harm the coyote except by going 'beep, beep.' "
"2. No outside force can harm the coyote -- only his own ineptitude or the failure of Acme products."
"3. The coyote could stop anytime -- if he was not a fanatic. (Repeat: 'A fanatic is one who redoubles his effort when he has forgotten his aim.' -- George Santayana.) "
"4. No dialogue ever, except 'beep, beep.'"
"5. The road runner must stay on the road – otherwise, logically, he would not be called road runner."
"6. All action must be confined to the natural environment of the two characters -- the southwest American desert."
"7. All materials, tools, weapons, or mechanical conveniences must be obtained from the Acme Corporation."
"8. Whenever possible, make gravity the coyote's greatest enemy."
"9. The coyote is always more humiliated than harmed by his failures."
Such lists of creativity-enhancing constraints could also be compiled for other worlds fashioned by comic geniuses, such as the Astérix cartoons scripted by René Goscinny, or the Don Camillo stories of Giovannino Guareschi, wherin the reader's expectations are always satisfyingly yet never-quite-predictably met.
The third rule's my favorite: other fanatics, in Santayana's sense, include Don Quixote, Captain Ahab, Basil Fawlty, Father Ted, and Doctor Doofenshmirtz...