It wasn't quite a New Year's resolution that propelled William Hickling Prescott forward in writing his history of Peru — it was a bet. His friend Edmund B. Otis had wagered $50 that Prescott could not write 100 pages in 100 days. After that 100 days was over, the bet was renewed for another 100 days until writing was finished.
But it was not mere laziness that was slowing down the project. "If I can once get in harness and work I shall do well," Prescott wrote, "but my joints are stiff, I think, as I grow old." The bet was his motivation. "Shame on me if I fail."
On January 11, 1846, a journal entry gives an update on his progress: "A miracle — I have kept my resolve thus far and been industrious three whole days! Now, meliora spero." (Translation: "I am better"). By then, Prescott was only 49 years old, but not in the best health. His eyes were always a concern. After an accident while a student at Harvard, he had lost sight in one eye and too much work left him blind in the other one as well.
Prescott's efforts were also hampered by a lack of interest in his subject, which he concluded was "second-rate." Still, he worked hard. By April, he admitted the book's "great defect is want of unity." He hoped the book would read like an adventure tale alone the lines of the Iliad, though he earlier warned himself, "It would not be decent, nor politic, to turn out histories like romances." Finally, in 1847, Prescott's History of the Conquest of Peru was published in two volumes. I haven't found for sure how much Otis paid him for its completion.