Crimson Longinus
Legend
As a Player, I get my fun both from overcoming challenges but also from leaning into the weaknesses of my character to drive the story in unexpected directions. I have fun making sub-optimal decisions that seem in-character, even if it complicates things for myself and the other PCs.
Does that persuade you that it's fine to leave resolution of social interactions to the whim of the player? (I suspect not.)
One way to encourage people to play this way is reward the players with XP/inspiration/fatepoints/etc when they play their character's flaws. Personally I'm not the biggest fan of this and I don't think this sort of bribery is generally necessary with good players, but it is definitely much better and way less obtrusive than mechanics that compel the PC to behave in certain way.