Who said 'Every human creature is constituted to be that profound secret and mystery to every other'?

Charles Dickens, in his book:- 'A Tale of Two Cities', Book the First: - 'Recalled To Life', Chapter 3 - 'The Night Shadows', first line:

"A WONDERFUL FACT to reflect upon, that every human creature is constituted to be that profound secret and mystery to every other."

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