In my eyes, a novel premise generally has four parts:
- What concrete, specific thing does the character want? -- This is the objective they'll pursue throughout the book.
- What internal need drives that desire? -- This is the human motivation that makes that objective so important. Usually it's something very simple: a desire for love or respect or power.
- Why is that desire the most powerful force in the main character's life? -- Every human has all the various human desires. But in some people, finding love is the most important. For others, it's gaining social status. Still others prioritize avoiding pain. This element is, by far, the most difficult to provide, because it's the most artificial. In real life, we don't know why people are the way they are. But in fiction, you have to provide a reason. Usually, it's situated somewhere in the backstory. Something happened in their past and it somehow hurt them, and now they need to fix that hurt.
- What do they have to lose? -- This is the thing holding them back--the reason they haven't just gone for it.
With these four elements, I can start to develop the rest of the novel: the plot, the conflicts, the narrative and counternarrative.
Of these four things, I think the first is the most important. You can develop a really compelling character with a really compelling desire, but if you can't provide them with an inherently dramatic external objective, then you have no novel. And that's not easy. Most external desires aren't very dramatic. Everything in the world might hinge, in the character's mind, on them having a successful opening for their restaurant...but how are you going to write a novel about that? For one thing, how do you measure success? It's something that happens over time. There's no climax there.
If you want to write this story, then you need to figure out where exactly in the restaurant business there might be some kind of breakpoint. For instance, maybe their boss is selling off the place, and they really want to buy it. In that case you have something dramatic: a thing can be acquired or lost in a moment. But even there, it's a bit ehh, because why does it need to be this restaurant? What's at stake? If they don't acquire it, then who cares? If you're trying to write this story, then you're going to have to do so much additional work in order to make any of it matter.
Whereas if you start with a compelling objective, then I think you've done 50% of the work. Oftentimes it's incredibly difficult to maneuver the other pieces into place: figuring out why a person would want something isn't easy, particularly when the thing they want is not a normal thing for a person to want. But none of that stuff needs to be unique. Like I said, none of these desires are unique to any person--it's how they choose to fulfill those desires that's unique. And if your mode of fulfillment is special, then you don't need to work as hard to give the character a special backstory.