1. A strong religious faith that erred on the side of compassion and deep caring for other people's well-being.
2.The sort of curiosity about how the world worked that you might expect form the son of a wheelwright.
3. A work ethic that made it possible for Haydn to write an astonishingly large body of work.
4. Musical talent
The first quality expressed itself in music that aimed to help lift the spirits of people who were feeling down. Haydn's concern for other people made him the perfect person to give feedback to, as large numbers of people did. He wanted to know how his music was being received, and he wasn't all that concerned about what class his listeners belonged to. At the same time, he stood up for himself, as a famous anecdote shows: when one of the Esterhazy princes tried to tell him how to run his rehearsals, he told the man off, saying that the rehearsal was Haydn's domain. Haydn was given the name "Papa" as a term of endearment. In numerous ways he endeared himself to his musicians, in the process getting them to give the best that they had in them.
Th second quality gave Haydn a shot at immortality, as it brought out the best that was in him. He could not be satisfied with a piece until he had brought out its full potential. This meant eschewing any sort of formula, with the exception that Haydn invented sonata form to give a general structure to his music. But within that framework, the listener never really knows what to expect from a Haydn piece when hearing it for the first time. And yet, even on repeat listening, Haydn's inventiveness and thoroughness make it possible to hear things that one had not heard in previous hearings.
The work ethic made it possible for Haydn to satisfy the many requests he received from people who wanted more music from him. Given that he didn't have more hours in the day than anyone else, some people basically cheated and went to lesser talents and persuaded them to *claim* that Haydn had written the pieces. This has complicated efforts to figure out which pieces were really by Haydn, and which were not.
Finally, it can't be denied that, by some genetic and evolutionary coincidence, Haydn's parents passed musical talent to their children. Of the five Haydn siblings who survived to adulthood, three made music their life's work. Johann Michael Haydn worked as composer and musician all his working life. He was an early influence on Mozart, and he also taught Carl Maria Von Weber. Johann Evangelist Haydn seems to have lacked the ambition to write music, but he was apparently a fine singer. All three Haydn brothers sang as choirboys in Vienna. But unlike Joseph and Michael, Johann Evangelist also trained as a wheelwright, like his father. But the bottom line is that the three brothers had fine musical ears and a desire to make music. Musical talent is sometimes said to take second place to perseverance. 10,000 hours of practice is what it takes to become a world-class musician, assuming that you meet the threshold of basic aptitude. The perseverance was there by both nature and nurture. The musical ear was there, too. A good ear is the ingredient without which one cannot hope to become a successful musician. The Haydn brothers had it. They just did.
Taken together, these qualities made Haydn relatively popular as musician/composers go. Some people liked him because of his generosity and his willingness to listen to their concerns. There would have been people who did *not* like him (you can't please everybody), but there have been contemporaneous anecdotes about people who considered both Haydn and Mozart to be silly men, but Haydn could nonetheless be respected because of his sincere religious faith. After his late oratorios became famous throughout Europe, Haydn was always eager to hear from representatives of the many amateur choral societies that sprang up to perform these and other works. This had the effect of creating a virtuous circle. People whop wanted to form choral societies knew that they could count on a sympathetic ear if they approached Haydn.