Sometimes, the error is all about using the wrong word.
Google definition of fastidious, and this is what you’ll get: 1. very attentive to and concerned with accuracy and detail. 2. very concerned with matters of cleanliness. Synonyms: scrupulous, fussy, critical, nitpicking…
Doesn’t sound like the sort of thing Heart (a cartoon personification of the fun-and-feelings aspect of personality) would say about its preferences concerning the world and why it likes fantasy better, does it? If anything, you’d expect Brain (the logic-and-routine aspect) to have fastidious tastes, a demand for order and tidiness… which isn’t what you get in a fantasy world, last time I checked.
If you keep a pet thesaurus, you should also have a dictionary to help it learn good behavior. 🙂 A synonym is a word with a similar meaning, not the same meaning (that would be a homonym, and English has few of those), so you need to make sure you know the precise definitions and pick which word out of a thesaurus list actually means what you intend it to mean.