Linguist Daniel Everett went to Brazil as a young Christian missionary to work with the Pirahã indigenous people. Instead of converting them he lost his faith and his family, and provoked a major intellectual row.

“They lived so well without religion and they were so happy. Also they didn’t believe what I was saying because I didn’t have evidence for it, and that made me think. They would try so hard to understand what I was saying, but it was obviously utterly irrelevant to them. I began to think: what am I doing here, giving them these 2000-year-old concepts when everything of value I can think of to communicate to them they already have?”

Daniel Everett Interview: Out on a limb over language (NewScientist.com)

Read Don’t Sleep, There Are Snakes: Life and Language in the Amazonian Jungle by Daniel L. Everett