https://archive.is/E5FMW

"People have often asked me what moves me most," said Tolkien. "I think the most tragic point in the whole story is the terrible irony that good often does evil. The most tragic moment is when Sam in his protectiveness says, 'Take your hands off.' And therefore defeats Gollum's repentance. Because that seems to be very true to life." Although Sam is only trying to protect his friend, his action causes Gollum to revert to his evil side. This speaks to Tolkien's wider world view, says Lee. "What happens in his mythology is that good can sometimes do excessive evil unintentionally."

It's always a pleasure to read more about his thoughts of his own books. Of his works I still enjoy The Hobbit the most, but there's so much to read into all of it.

For those unfamiliar, Tolkien was a devout Roman Catholic. His choice of "most tragic moment" very much reflects that worldview.