This.
I see a lot of complaining about how it doesn't make sense that Kylo Ren got whooped by Rey (or that she put up a "competent" fight). I think there are two reasons to this and the movie seemed pretty clear about it to me.
1. Kylo Ren isn't good, period. He is obsessed with being Darth Vader, and is delusional about his own power. He commands no respect from his peers and he's completely unhinged. Why? Because he has his own internal struggles about how weak he is. He knows he's a fraud, he knows he is nowhere near worthy of his grandfather. He falls apart in that final confrontation because he is being exposed, he's fighting against someone who has the same potential power as him and he gets a harsh reality check. He's basically a force-sensitive bully in a world where no one has ever been able to fight back. He's only fought normies.
2. Between what happened in the movie and the fact that the title is "The Force Awakens', I don't believe that Rey is a nobody. I think her force-powers are dormant, and have been repressed. There's more to her backstory, they wouldn't have foreshadowed/referenced her past if it wasn't vital to the plot.