A wonderful fact to reflect upon, that every human creature is constituted to be that profound secret and mystery to every other. A solemn consideration, when I enter a great city by night, that every one of those darkly clustered houses encloses its own secret; that every room in every one of them encloses its own secret; that every beating heart in the hundreds of thousands of breasts there, is, in some of its imaginings, a secret to the heart nearest it!
Something of the awfulness, even of Death itself, is referable to this. No more can I turn the leaves of this dear book that I loved, and vainly hope in time to read it all. No more can I look into the depths of this unfathomable water, wherein, as momentary lights glanced into it, I have had glimpses of buried treasure and other things submerged. It was appointed that the book should shut with a spring, for ever and for ever, when I had read but a page. It was appointed that the water should be locked in an eternal frost, when the light was playing on its surface, and I stood in ignorance on the shore.
Charles Dickens, A Tale of Two Cities
Painting: John William Waterhouse, Ophelia (1910)
Unfathomable: adj; 1) Too deep to be measured; 2) Impossible to understand for being mysterious or complicated.