“Stimulus must be external – that is, action or dialogue, something that could be witnessed if the transaction were on a stage. Response must also be external in the same way. For every stimulus, you must show a response. For every desired response, you must provide a stimulus. Response usually must follow stimulus at once. When response to stimulus is not logical on the surface, you must ordinarily explain it. A few examples should make these rules clearer in your mind. Let’s suppose you have a segment in your story where Joe and Sam are playing catch with a baseball in the front yard. If you show the following stimulus – Joe threw the ball to Sam. Then you must show Sam’s response, such as – Sam caught it. (or)
Sam dropped it. (or)
Sam didn’t see it and it hit him in the nose. Or something of a similar, immediate response-nature. How can something as simple as this get messed up? One sees it messed up all the time. Consider this transaction: (Stimulus) Joe threw the ball to Sam.
“Sure is a nice day!” Sam said. Now, some might think this is fine, because the reader will assume that Sam caught the ball. I’m afraid that many, many readers, however, will not make that assumption, and a tiny tickle of disbelief will begin far back in their brain somewhere – the obvious question: What happened to the ball??? How do you fix such slips? By showing the completion of the stimulus-response transaction, by providing the response to the stimulus you’ve already shown, thus: (Stimulus) Joe threw the ball to Sam.
(Response) Sam caught it. “Sure is a nice day to play catch!”