I remember seeing the movie Split. Spoiler alert! It’s basically about a man that goes crazy because of childhood abuse, captures 3 girls, kills two of them, but leaves the one alone as he learns that she’s also has a rough childhood. Right before he changes his mind about killing her he says «your heart is pure» before leaving her be. And she was indeed the nices of the three girls. I think the producer wanted to say that you become more compassionate as you go thought shit in your life. In our case this is stuttering.