Rory's downfall is a result of her entitlement and inability to take accountability. Episode 21 Season 2 really shows us this for on of the first times and is the pinpoint of her downfall.

RORY tells her mother the truth, she continually claims that she feels as if she’s a victim to some outside force or health condition. She basically plays into what people have been saying is wrong with her from the beginning. -That she’s so whipped by this guy that she would make idiotic rash decisions that cause her to shrink on her responsibilities and throw everything away for the perspective of and life of the man she’s interested in.