Plot-Sensitive Snooping Skills

"Superman: What's with them? Green Lantern: Man, for someone with like fifty different kinds of vision, you are so blind."

- Justice League Unlimited, Kid Stuff

A character who shows incredible insight into the minds of strangers is more or less blind to the secrets of his or her own inner circle. This is generally done because the writers want it that way; if the character were to learn the motivations of his/her nearest and dearest, the series would run out of material a good ten or twelve episodes early. The character is not unobservant, per se, but is only really capable of guessing whatever the writer wants him or her to guess - and that rarely includes devastating revelations that have a personal effect on the guesser or that would cause an untimely plot twist. A requirement for the Chaste Hero.

A kind of involuntary Selective Obliviousness, insofar as it is not an intentional refusal to guess at (or acknowledge) the truth. Also a frequent cause of Failed a Spot Check.

Anime and Manga

 * Usagi from Sailor Moon is a particularly Egregious case. A number of one-shot characters fail to hide their innermost secrets from her, but she never notices her little brother's crush on Ami in the fourth season Beach Episode.

Film

 * Film example: Robert DeNiro's character in Meet the Parents, who discovers all sorts of unsavory things about his future son in law, but has no clue (even when said clues are waved in his face) that his own son smokes pot.
 * He also comes to some incorrect conclusions because he didn't bother to deconflict the different people with the same name, a mistake that is only possible if everyone involved ignores the fact that there might be more than one person with his same (or similar) name.

Literature

 * In Sonya Sones's young adult novel One of Those Hideous Books Where the Mother Dies, Ruby claims that, like her mother, she has a "gaydar" that's never wrong in detecting gay people. Her gaydar leads her to believe that Max, one of the workers for her father, is gay, which turns out to be right on the mark, but completely fails in regards to

Live Action Television

 * Chloe in early Smallville.
 * The television show Profiler, and every show like it. Sure, she can look at a handful of clues and figure out why the killer liked the color purple (or whatever), but she can't look at years of evidence and figure out who has a crush on her, or what her daughter is up to, or anything personal.
 * Kate (and to some extent, nearly everyone) on NCIS. Kate is supposed to be an amazing profiler because of her Secret Service training, but she was the most oblivious person on the team until McGee showed up.
 * You would think the profilers on Criminal Minds are a justified example, since they have a rule about not profiling each-other but their camaraderie is so strong that they really can't keep secrets from the team for long and they all are basically each-other's therapists.
 * Frasier on Due South, having been Raised by Wolves.

Other

 * Pretty much any reporter or detective supporting character of a superhero.
 * But not always. It's implied that Commissioner Gordon has a pretty good idea as to who Batman really is, but he doesn't attempt to prove this, because if he officially knew who Gotham's top vigilante was, he'd be obliged to do something about him. During No Man's Land, Batman removed his mask but Gordon kept his eyes closed (no, really). Batman strongly suspects that Perry White figured out that Clark Kent is Superman quite some time ago and has chosen to keep silent.
 * In Batman Year One, it's all but said that Gordon knows. As his partner points out, he's the only one in Gotham with the time and money. But there's no evidence, just a convenient collection of alibis and 'accidental injuries' right where Batman would have them.
 * This leads to the I Know You Know I Know scene at the climax when Batman (out of costume) saves Gordon's son. Gordon conveniently blames the loss of his glasses for preventing him from recognizing the man standing no more than two feet away from him who hands him the child. Batman made no attempt to hide his identity, and clearly recognizes that Gordon is willing to protect his secret.