"The difference between a short story and a novel" by Philip K. Dick

 "The difference between a short story and a novel comes to this...."

"It is in sf stories that sf action occurs; it is in sf novels the worlds occur.... Crisis is the key to story-writing,a sort of brinkmanship in which the author mires his characters in happening so sticky as to seem impossible of solution. And then he gets them out... usually.... But in a novel the actions are so deeply rooted in the personality of the main character that to extricate him the author would have to go back and rewrite his character. This need not happen in a story, especially a short one.... [T]his makes clear why some writers can write stories but not novels, or novels but not stories.... [A]nything can happen in a story; the author merely tailors his character to the event.... As a writer builds up a novel-length piece it slowly begins to imprison him, to take away his freedom; his own characters are taking over and doing what they want to do--not what he would like them to do. This is one one hand the strength of the novel and on the other its weakness."

--Philip K. Dick, The Collected Stories of Philip K. Dick [originally 1968, so probably from the 1969 collection, The Preserving Machine.