This is Nostromo's ideal of reputation again, but now in reference to the "sham"
life that must be maintained by keeping the one dark spot secret. Note that the
"essence, value, reality" of his life does not consist entirely of his
reputation; it also derives from his independent secret; this is new. "That
thing" is, symbolically, the knowledge of inner worth, a notion outside the
range of "common comprehension," i.e., collective, society-organizing
ideals.