After finishing your first novel, you can't find an agent to represent you and no publisher will accept an unsolicited manuscript. You've sent query letters to dozens of agents only to be rejected by every one of them. Your family and friends have gone from being your supporters to telling you that you must not be a good enough writer or the agents would've signed to represent you. Whatever the experts and pessimists tell you, don't let their comments influence you to throw away your dream. Keep sending out those query letters.
     While you wait for someone to finally decide to publish your novel, keep writing. Take the time you now have to re-read your novel and make improvements . . . if you feel it needs something more or less. No matter how many times you've proofread your manuscript, do it again. Once you've finished that, keep writing.
     But what more is there to write if you have a completed and polished manuscript? The answer is your next novel. Agents and publishers aren't looking for what the music industry refers to as "one hit wonders". Even if your first novel makes every best seller list and sells a million copies, especially then, people who enjoyed your novel will be eagerly awaiting your next great story. Write it now. If your stories have similar themes and not part of an on-going series, you might find your second or third book gets published first.
     If you're planning a series of novels in which the characters remain the same and the main plot or subplots carry over from one book to the next you have even more reason to keep writing. If an agent or publisher likes your idea for the series, some of them will probably be more interested in representing the series knowing either the second part or the entire series is complete. They know they won't have to wait years for the next installment and the next book can be scheduled for publication and release at any time.
     In the worst case scenario, your first book will never get published. Perhaps you really never had enough expertise or did enough research to write a great novel about fighting forest fires. Try your hand at writing a romance or science fiction novel. These aren't any easier to write, but you might just discover you can do a better job.
     Even if you give up on getting your book published. Keep writing, especially if you enjoy writing and telling a good story. If you've gone so far as to finish the first novel, chances are you really enjoy reading the book you've created. Share it with your family and friends. Pass it along to your children or grandchildren. Future generations will enjoy your novel even if it's only a very limited audience.