The Lost City of Z is the type of story that, if it were fiction, would probably having you throwing the book to the ground and saying, "Inconceivable!" In a novel, Grann would find Z, and Fawcett would be there, indulging in an elixir of eternal youth. Somehow, in fiction, that would be within the realm of believability.
Instead, we get one of the biggest anticlimaxes ever. Grann finds little more than a trace of Z. It's like if Indiana Jones never found the Ark of the Covenant but did maybe find a splinter that may have come from a box maybe touched by Moses.
Yeah, not quite the same thing.
However, as nonfiction, Grann is bound to the truth. It's great that the truth is sometimes stranger than fiction. Fawcett's story, especially, is inherently exciting and dramatic, and Grann draws vivid, round characters from the real-life historical figures. Grann's frame story is less about the destination and more about the journey.
We get to discover the world of the jungle and the people within it right alongside Grann—but without the mosquito bites.