I watched a Sylvester Stallone movie called Escape Plan a few months back that utilized a character type I’ve come to hate, which is a type of Mary Sue. This particular brand of Mary Sue, regardless of gender, annoys me because there is a certain body of knowledge people come with and tend to specialize in.
Can Sly be a prison architect? Sure. Can he literally write the book on prison architecture? Sure (even if it’s over the top). Can he know the habits of prisoners and analyze prisons for escape routes? Yes. Can he know how to use a sextant? Erm, maybe if he spent a lot of time sailing growing up. Can he MacGyver one into existence with materials he got from prison. No. Just no. Can he, using only a vague reading given to him by another prisoner who had no view of the horizon determine his latitude? No. Absolutely not.
This type of thing is becoming increasingly common in storytelling. Characters with expertise in every body of knowledge come forward to save the day with facts that only they could possibly possess.
To me the prototype for this kind of character is actually a historical and modern day favorite: Sherlock Holmes. His encyclopedic knowledge of everything removes most of the humanity from the character. No one can expect to know everything. Even Gregory House looked on with skepticism when a med student “expected [him] to know the kind of snake by the shape of the puncture.”
When characters like Sly enter the picture, with too much innate knowledge, I’m drawn out of the story. I can almost never get back into it, either. It’s why I can’t read Holmes any more, simply because of how preposterous it is that Holmes has this level of knowledge.
Data. Lt. Commander Data from Star Trek: The Next Generation can have this level of knowledge. That’s appropriate. That makes sense. But even data has to stop and learn something new. Even if it only takes him a few seconds to do so.