A sin takes on new and real terrors when there seems a chance that it is going to be found out. This gives it a fresh and most substantial and important aspect.

Mark Twain (1835–1910) American writer [pseud. of Samuel Clemens]
Story (1899-12), “The Man That Corrupted Hadleyburg,” ch. 4, Harper’s Monthly, Vol. 100, No. 595
    (Source)

(Source (Alternate)). First collected in The Man That Corrupted Hadleyburg and Other Stories and Essays (1900).