There is often a difference between what an audience expects and what logically must happen. A prime example occurs in the Laurel and Hardy film, The Music Box. Stan and Ollie are piano movers. The setup is their efforts to get a piano up a quarter mile flight of stairs to a hillside house. Every time they get to the top, one way or another it slides down to the bottom again. Finally, they get it up there only to discover the address is on the second floor! So, they rig a block and tackle and begin to hoist the piano up to the second floor window. The winch strains, the rope frays, the piano sways. And just when they get the piano up to the window, they push it inside without incident.
After the audience has been conditioned by the multiple efforts to get the piano up the stairs, pushing it in the window without mishap has the audience rolling in the aisles, as they say.
From the Dramatica Theory Book