Busy day...here's a couple of thoughts from others. This first one is probably either by Robbie McCauley or George Lanning. Either way, it aptly describes the short story vs. the novel:
A short story is like a flare sent into the sky. Suddenly and startlingly, it illuminates one portion of the world and the lives of a few people who are caught in the glare. The light is brief, intense, and contrasts are likely to be dramatic. Then it fades quickly and is gone. But, if it is worth its moment of brilliance, it will leave an enduring afterimage in the mind's eye of the beholder. In contrast, a novel has great luxuries of time and space. It can explore without hurry, develop inevitable currents of action, and watch its people change and mature.
This second one is definitely a rule for any writer to live by:
"Writing has laws of perspective, of light and shade just as a painting does, or music. If you are born knowing them, fine. If not, learn them. Then rearrange the rules to suit yourself."