"Prince Rhaegar loved his Lady Lyanna and thousands died for it. Daemon Blackfyre loved the first Daenerys, and rose in rebellion when denied her. Bittersteel and Bloodraven both loved Shiera Seastar and the Seven Kingdoms bled. The Prince of Dragonflies loved Jenny of Oldstones so much he cast aside a crown, and Westeros paid the bride price in corpses. All three of the sons of the fifth Aegon had wed for love in defiance of their father's wishes. And because that unlikely monarch had followed his heart when he chose his queen, he allowed his sons to have their way, making bitter enemies when he might have made fast friends. Treason and turmoil followed, as night follows day..."
— Ser Barristan Selmy, exposing many instances of the trope in-universe, starting by the most recent, A Song of Ice and Fire,
"How many tens of thousands had to die because Rhaegar chose your aunt?"
CK2 makes you really empathize with evil kings and see their point of view. Like, who is this ungrateful little shit who wants to pollute their lineage by marrying some commoner? How can they just disregard a thousand years of careful planned inheritance and eugenics for something as selfish as love? They're not even going to be alive in 100 years, their lives are so small and inconsequential compared to the dynasty.