Folly calls aloud,
Stolen water is sweet,
and bread eaten in secret is pleasant. (Proverbs 9:17)
The water is no different whether stolen or bought. Why does it taste different when stolen? Here is Augustine’s experience from his Confessions which are written as a prayer to God.
I was willing to steal, and steal I did, although I was not compelled by any lack, unless it were the lack of a sense of justice or a distaste for what was right and a greedy love of doing wrong. For of what I stole I already had plenty, and much better at that, and I had no wish to enjoy the things I coveted by stealing, but only to enjoy the theft itself and the sin.
There was a pear-tree near our vineyard, loaded with fruit that was attractive neither to look at nor to taste. Late one night a band of ruffians, myself included, when off to shake down the fruit and carry it away, for we had continued our games out of doors until well after dark, as was our pernicious habit. We took away an enormous quantity of pears, not to eat them, ourselves, but simply to throw them to the pigs. Perhaps we ate some of the, but our real pleasure consisted in doing something that was forbidden.
Look into my heart, O God, the same heart on which you took pity when it was in the depths of the abyss.... My soul was vicious and broke away from your safe keeping to seek its own destruction looking for no profit in disgrace but only for disgrace itself. (pp. 47-48)