From the back cover of Words of Radiance:
One would think that Shallan's broken soul would be the result of killing her mother (and then later father). However, Shallan was already surgebinding- it's why her mother tried to kill her in the first place.
Is a broken soul a prerequisite for spren bonding/surgebinding? Was Shallan's soul was already broken when her mother tried to kill her?
I think the picture she paints in chapter 45 in her discussion with Wit is interesting here. In that picture Shallan and her family definitely aren't broken.
Why didn't it happen that way? In her description:
It seems like her mother didn't love her in the first place (kind of obvious I guess if she was willing to kill her), and that's what caused Shallan's initial psychological trauma which allowed her to originally gain her powers.
