The story
A reference to the story in the Bible in which God tells Adam and Eve not to eat the forbidden fruit, but they are tempted by a serpent and do so anyway.
Etymology from Wiktionary, CC BY-SA 4.0.
forbidden fruit is the sweetest
Today it means: Forbidden things seem more appealing; people desire things more if (or, in some way, because) they can't have them. Full definition →