John Kennedy Toole is probably the exemplar of this, in that 'A Confederacy of Dunces' was unpublishable during his lifetime, but became the picaresque national narrative after a large push by Walker Percy to get it published a decade after Toole's death. It ended up winning the Pulitzer the following year.
Stoner, a novel by the American writer John Williams, is a lesser known but no less apt example. In 1963 Williams' own publisher questioned Stoner's potential to gain popularity and become a bestseller. It sold fewer than 2000 copies, and was out of print a year later.
After subsequently being discovered and championed by literary luminaries like John McGahern, it was republished and translated into several languages, selling hundreds of thousands of copies across 21 Countries. By 2013, the book had achieved international best-seller status. I'd urge anyone with a love for academia, literature, or modern bildungsromans to give it a go. To me it's effectively 'American Gothic - The Novel'
https://www.theguardian.com/books/2013/dec/13/stoner-john-wi...
It's the same in all creative professions, and even more so for those that grant visibility. I think most would be fine considering this activity as a part-time commitment, instead of chasing something that has little chance of coming true. Of course, you can't be a part-time athlete and aspire to greatness, but I don't think the same applies to writing, for example.
Now, we are in the realm of anecdotes, but the novel “Il Gattopardo,” which I consider to be among the top three Italian, and perhaps European, novels of the 20th century, was written by an amateur who did not even send the manuscript out to be considered for publication. It was discovered after Tomasi di Lampedusa's death by Giorgio Bassani, a talented writer who did not write full-time and who had incredible success with some fantastic novels, such as "Il giardino dei Finzi-Contini" (The Garden of the Finzi-Continis).