I hate when people say, 'Oh, they laughed all the way to the bank.' That's nonsense because the most cynical, unhappy people are Hollywood screenwriters. They earn hundreds of thousands of dollars a year for work that's never made.
For a novelist, no matter what, it's a complete work, even if it's not published. But if you write a screenplay, and it's not performed, then it's a sad and frustrating experience.
Whether you're an obstetrician or a third-grade teacher or a real estate agent, you know when you're doing good work. You're passionate about it.