Here's a breakdown of the factors that likely contributed:
* His personality: Hemingway was known for his strong personality, his guidance to younger writers, and his often authoritative presence.
* His writing style: His writing was often direct, clear, and powerful, which could have contributed to a perception of "fatherly wisdom."
* His life experiences: He was a war correspondent, a fisherman, a hunter, and a traveler, all experiences that would likely have imbued him with an air of authority.
* His interaction with others: It was likely that younger writers and friends began calling him "Papa" as a term of endearment and respect for his guidance and wisdom.
It's important to note that there is no single book or event that definitively led to the nickname "Papa." It was a gradual process that stemmed from Hemingway's personality, writing, and experiences.