Them: I have a great idea for a story! It's about a regular person who no one takes very seriously. After strange and sinister things start happening around town, they get caught up in a quest, and have to leave everything they’ve ever known in order to prevent a terrible calamity from coming
to pass. Along the way, they make friends and enemies, take a few licks, and give some in return, becoming more independent and wise, and gaining insight about the world they didn't have before, which ultimately makes them a better person. When they finally return home, everyone sees just how much stronger they are, and they finally gain the respect of their kith and kin, more or less living happily ever after. The end.
Me: Wow! Boy, does that ever sound great—I'm sure you'll hammer out the details as you go along. So, you have the basics of it; now, what is it?
Them: What do you mean? I just told you.
Me: You told me the substance, but you haven't expressed the form. Is it a novel? Perhaps a screenplay? An episodic tv show? One-act play? Three-act play? Five-act play? Animation? Comedy sketch? Lyric poem? The form is going to determine to what extent you’re going to be able to extrapolate on your subject. We won't even discuss genre at this point.
Them: Tell me more about form.
Me: I'll use the analogy of water. If you are the water-bearer, the substance of your story is the water, and the vessel you pour the story-substance into is the form. We understand that water has the property of filling whatever volume of space it is poured into to the point that it can. If the vessel is too large, the water spreads out to fill the vessel, but cannot, so the substance lacks depth. If the vessel is too small, the water overflows the container, and thus there is a great deal of waste. If, however, you fit your form to the substance of your story, you find balance and parity. This can work the other way as well: either from the inside-out, or the outside-in. Since it is suited to the form it is designed for, the water will not over-flow and become messy, nor will it lack requisite depth.
Them: But how do I know how to measure that?
Me: Open your kitchen cabinet: inside you find a teacup, a pint glass, a liter mug, and a three gallon cooking pot. The substance of your story must be drunk according to the vessel chosen. If your story has little definition, but a lot of punch, you may only need a teacup full: Setup/hook/ punchline. Done. This is what a comedy sketch or short animation does. If however, your story requires great exploration of character motivation, or a highly detailed and individuated world, you may very well need that huge cooking pot. This is the stuff of great novels and prestige episodic television.
Them: I think I understand what you're saying, and will try to match my substance with the proper form. I do think however, that you use strange metaphors sometimes.
Me: That’s because the substance of what I’m saying requires the proper metaform. Them: (Sigh…)