Warning: Spoilers for Game of Thrones below!
The third episode of Game of Thrones, "The Queen's Justice," has a few shockingly memorable moments (like Daenerys and Jon Snow FINALLY meeting, for starters), but the quiet scene in the episode's final minutes is by far its most affecting. The celebration of Daenerys's Unsullied army easily taking Casterly Rock from the Lannisters is short-lived, since Jaime fakes them out by having Euron's fleet burn most of the Unsullied's ships and moves almost all of the Lannister forces to Highgarden instead. There, they quickly overpower House Tyrell, and Jaime has a tense one-on-one chat with Lady Olenna. It's during this conversation that Jaime reveals that he actually stole the savvy tactical move from one of his former enemies: Robb Stark.
After Olenna notes that Jaime took his army "and went where they weren't," he replies, "As Robb Stark did to me at Whispering Wood. There are always lessons in failures." (Which prompts a signature quip from Olenna: "You must be very wise by now.") The incident he references is the Battle of the Whispering Wood, which takes place in season one.
As you might recall, Catelyn Stark negotiates with Lord Walder Frey to allow Robb's army to pass across the Trident at the Twins, as long as Robb agrees to marry one of his daughters. They strike a deal (which is eventually broken and leads to the blood-soaked Red Wedding), and the Stark forces cross the river and split in two, with one half moving south to fight Tywin Lannister's army in the Battle of the Green Fork, and the other half going on in secret to confront Jaime.
Since Tywin thinks the whole Stark army is on its way to attack him at Green Fork, he has most of his men at the ready. The Lannisters defeat the Starks, but it's not until it's too late that Tywin realises Robb outsmarted him. Jaime, unaware of what happened to his father, is lured into the Whispering Wood by the rest of Robb's forces, northwest of Riverrun, and is swiftly defeated by the Starks. He's soon taken prisoner, and the Lannister army's presence within the Riverlands is almost entirely destroyed.
Although Jaime pulls the same clever manoeuvre in season seven's third episode, he's going to need a lot more tricks up his sleeve to defeat the Dragon Queen once and for all. For her part, Dany will have to learn from her own failures next week, judging from the nail-biting preview for episode four.