in so many words, it was one of the first questions my agent asked me.
and it's a question you WANT to be asked... because if people don't like your writing, they won't be asking to see more.
you want agents, editors and especially readers to always being asking:
"what else ya got?"
in fact, if you're very lucky, you will get this question so fast and frequent you won't be able to keep up with the demand. (unless you are one of those freaky fast writers who churn out books in a matter of days. man, i
it is possible you have just one great story to tell, one opus that will soar into literary history and make you a household name without ever writing another word. or perhaps you are in it for the money and are just talented and lucky enough to pull it off - that impossible 7-figure debut. if you achieve those goals and feel finished, then by all means retire and enjoy!
but if you're like me, you have way too many voices in your head to write just one. when i go on sub, if editors ask "what else ya got," and i have only empty hands to show them, i won't feel like i'm letting the editors down; i'll feel like i'm letting my characters down. each of them deserves a story. now, whether that story ends up in a trunk or on sub is a very different matter. i love Trapper, Andi, Boston and Tuna, but 'kids, get comfy. you're gonna be in that trunk for a looooong time.'
so now i'm hard at work telling the story of my two new favorite characters and hoping i do them justice... because there's a tiny bit of pressure in that question of what else you have cooking - this itty bitty, unspoken sub-question:
"and is it better?"
if you're learning and growing and pushing yourself as an author, the answer should probably always be, "yes, it's better." but when you're going from working on a revised, polished, finished manuscript to a new rough draft, it's kinda hard to see much that's better.
the point is to keep writing. work on one project at a time if you must (i certainly do), and work it until it's sparkling. you can even take a break afterward. but then push that diamond away (preferably in the direction of an agent or editor) and get back to digging through the dirt for the next rock you can polish into something precious. KEEP WRITING.