"Thou Hast Seen Nothing Yet"
Context: Amadis of Gaul, disdained by the Lady Oriana, left civilization to do penance on the Poor Rock. Don Quixote decides to follow his example, as well as that of Orlando Furioso when Angelica found another love. He orders Sancho to watch him for three days and then go to Dulcinea del Toboso to report to her to what extremes of madness her disdain has driven Don Quixote. Sancho protests. "Bless my eyesight, what can I see more than I have seen already?" In his reply, the Knight of the Sorrowful Countenance expresses more grammatically our slangy term, "You ain't seen nothing yet!"
Thou hast seen nothing yet . . . thou must see me throw away my armor, tear my clothes, knock my head against the rocks, and do a thousand other things of that kind, that will fill thee with astonishment.