The Cake Is a Lie

Sansa Stark in A Song of Ice and Fire
Sansa of House Stark is a main character throughout a lot of the famous book and TV series by George R. R. Martin. Oldest daughter of Eddard Stark, at the beginning of the series she is eleven years old, and slated to become the next Queen.

She is often regarded as a 'wide-eyed idealist', or someone who is too idealistic for their own good, due to the fact that her main flaw is her naivete. She often believes that the harsh and cold world around her works much like it does in romantic fairytales. She does eventually grow to become more savvy, cynical, and manipulative, despite constantly being the damsel in distress.

No True Scotsman
This fallacy comes about when; The goal of this fallacy is to ignore the fact that some members of a group may have characteristics that are undesirable, and enforce a purity standard on that group by excluding people who have any of these undesirable characteristics from the definition.
 * a universal claim is refuted
 * the claim is altered by going from universal to specific
 * the definition of a word is changed to make a claim true by default
 * a word is given a biased definition

Case Study
Despite all of the horrible things that have happened to Sansa over the course of the series, the countless times that she has been the 'damsel in distress', she often still believes that in her world there are such things as 'Knights in Shining Armor'. Even though she is presented with evidence that many knights are just thugs with swords, she has declared that any knight who doesn't live up to her often unrealistic expectations, as well as their vows to protect the innocent, is obviously "no true knight." - thoughts of Sansa Stark

To become a "True Knight" in Westeros, you have to make certain vows to protect the innocent, fight with honor, protect women and so forth. However, in this setting, it might be more accurate to say that "true knights" are actually in the minority. Regardless, Sansa seems to stick to her feelings about 'true knights', even after eventually recognizing that true knights, if they exist at all, are very rare. Sansa seems to (or did) recognize Gregor Clegane, or The Mountain, as a true knight, despite what he confesses he did to Elia Martell later on in the series.