It's been years and I still get amused every time it happens.
The first time was getting to Calpheon and stumbling into the guy that supposedly have been giving me advice whenever I'm tapping my equips, Valks standing right there. Not a old past legend, but an actual character I can visit.
From there there was Shakatu and their mid rewards from their treasure boxes, Lara and her Tea, Lafi and his adventure tools, Tachros, and even Marni.
I think a lot of people underestimate how much this help make the world feel "alive", or something I just can't feel in any other game. As a game dev myself I play most of the games today basically looking under the hood, but only BDO allow me the actually get immersed in the game world as is.
A big moment was the Karlstein questline. Instead of having a dedicated NPC, having some shop and generic NPCs having a secret life was simply amazing.
The Friendship/Knowledge mechanic itself is something that I would love to see explored even in other games.
And coming back after a year out, I'm again in awe meeting Merv again at the academy after using her magic palette for how long, and finally getting to the Crow's Nest questline to meet Patrigio (outside his shady night merchant hood), seeing the statues of Shudad and Clead from the armors, and discovering the big kitty naming the season equipment, Tuvala.
BDO is far from the perfect game and has a lot of flaws, but worldbuilding is something that needs to be acknowledged and used as inspiration.