Luke had feared her power. She tapped into the dark side too easily, he said. It drew her in, and she didn't even try to avoid it.
Or at least that was then. Now, standing by Kylo Ren's side, the dark side didn't come so easily. "I can't do this," she confessed to Kylo. "I still feel the pull of the light."
Kylo was struggling with the same conflict between light and dark. "You're just new to it. You'll figure it out."
So, Rey kept at it, but the light side still called to her, as it did to Kylo.