Pilgrim's Progress

The mire couldn't be mended because it was a place of collected sin.

And he said unto me, This miry slough is such a place as cannot be mended; it is the descent whither the scum and filth that attends conviction for sin doth continually run, and therefore it is called the Slough of Despond; for still, as the sinner is awakened about his lost condition, there ariseth in his soul many fears, and doubts, and discouraging apprehensions, which all of them get together, and settle in this place. And this is the reason of the badness of this ground.