There is no friend as loyal as a book.
A short story is a sprint, a novel is a marathon. Sprinters have seconds to get from here to there and then they are finished. Marathoners have to carefully pace themselves so that they don't run out of energy (or in the case of the novelist-- ideas) because they have so far to run. To mix the metaphor, writing a short story is like having a short intense affair, whereas writing a novel is like a long rich marriage.