V.e. Schwab said this quote

“ Because Rhy didn’t need his protection, not anymore, and he’d only told a partial truth when he said they both needed this.The whole truth was, Rhy needed it more.Because Kell had given him a gift he did not want, could never repay.He’d always envied his brother ’s strength.And now, in a horrible way, it was his.He was immortal.And he hated it.And he hated that he hated it. Hated that he’d become the thing he never wanted to be, a burden to his brother, a source of pain and suffering, a prison. Hated that if he’d had a choice, he would have said no. Hated that he was grateful he hadn’t had a choice, because he wanted to live, even if he didn’t deserve to.But most of all, Rhy hated the way his living changed how Kell lived, the way his brother moved through life as if it were suddenly fragile. The black stone, and whatever lived inside it, and for a time in Kell, had changed his brother, woken something restless, something reckless. Rhy wanted to shout, to shake Kell and tell him not to shy away from danger on his account, but charge toward it, even if it meant getting hurt.Because Rhy deserved that pain.He could see his brother suffocating beneath the weight of it. Of him.And he hated it.And this gesture—this foolish, mad, dangerous gesture—was the best he could do.The most he could do. ”