Stolen fruit is (the) sweetest proverb
People tend to like forbidden or illegal things just because they are forbidden or illegal.
Though he has money to buy fruit, he loves picking fruits surreptitiously from his neighbor's garden. Stolen fruit is the sweetest, I guess.
Although his wife is beautiful, he still has an affair with another woman. I think it's just because stolen fruit is sweetest.
The origin of this proverb originates from the Bible, when God forbade Adam from eating a certain fruit, an apple. Satan persuaded Adam and Eve that the fruit was the sweetest and that they had to try it. After eating this forbidden fruit, Adam and Eve were expelled out of the Garden of Eden, according to the Bible.