Ben Solo grew up not hearing the full story of his family's heroic (and not so heroic...) exploits. He only knew bits and pieces until he was twelve or so. The adults around him freely referenced the past, not realizing how much of it he was actually hearing.

One day, he asks his parents or they finally decide to give him the full story. 'How I Met Your Mother' style. It takes hours, maybe even days.

Poor Ben's brain becomes mush somewhere in the middle. His suffering hits the max when they get to rescuing Han from Jabba. He's too catatonically horrified to appreciate Vader's heroic self-sacrifice. He's pretty sure he's delirious when his parents go on about Ewoks defeating Stormtroopers.

Bonuses:
+ This is why Ben Solo becomes Kylo Ren.
+ Han and Leia trying to tell the story together. They keep going off into tangents and gently arguing about timelines and facts. Maybe they "take a break" at one point (reminiscing about Hoth or their "I love you./"I know." moment?) and poor Ben knows all too well what that shared look means (time to leave the house or wear HIMYM-style sensory deprivation headphones and goggles).
+ Luke, Chewie, the droids, or Lando adding their two cents and making it even worse.
+ Ben's future self retelling the story to someone else, who completely understands his reaction.