Case in point: recently for a piece I've been working on, I went back to one of Tolkien's statements we don't know first hand, or even second hand, but only third hand. I first learned about it from a quote in Marjorie Burns' excellent book PERILOUS REALMS, in which she quotes George Sayer as saying the following about "[Tolkien's] reaction to the Irish landscape":
"In a 1979 transcription of a discussion
on J. R. R. Tolkien and C. S. Lewis,
George Sayer tells a remarkable story
about Tolkien describing Ireland as
'naturally evil.' He could 'feel,' Sayer relates,
'evil coming up from the earth,
from the peat bogs, from the clumps of trees,
even from the cliffs, and this evil
was only held in check by the great
devotion of the southern Irish
to their religion.' "
--Burns, PERILOUS REALMS, page 19*
Unfortunately, as I said, we don't have any place where Tolkien himself wrote down anything like this, at least not that I know of. Nor did Sayer ever put this in his books or one of his memoirs, that I've been able to find. Our sole source for this seems to be a three-way discussion between Sayer, Humphrey Carpenter, and Clyde Kilby that took place at Wheaton in September 1979 -- and, just to complicate things a little further, no copy of the original audiotape of the event seems to survive, only a transcription published in a fanzine a few months later (the January 1980 issue of MINAS TIRITH EVENING STAR).
So there it is: a striking statement, entirely devoid of context, which we only have by a somewhat indirect route. No way to tell how serious Tolkien was when he said it, or how accurately our third-hand record of it represents his thought. But intriguing nonetheless.