"Sherlock in particular."

TV TV Tropes now has a page on Sherlock. It's immense:

"Ping Pong Naïveté:
Sherlock in particular. In A Study in Pink he remarks that the abandoned partner in a breakup will keep things for "sentiment", but in The Hounds of Baskerville five episodes later, John has to explain what sentiment is. Similarly, in The Blind Banker, he understands from subtle cues that a victim was sleeping with his PA, but in the same episode, John has to explain to him what a date is. And even then he doesn't know better than to crash one of John's. In The Blind Banker he deliberately charms Molly Hooper to manipulate her. It seems from this that he's aware she has a crush on him; in A Scandal in Belgravia he appears to be genuinely gobsmacked when he realises in the middle of a Christmas party that she does have a thing for him, meaning that although he's the world's most observant person, he's missed that she's been throwing herself at him for four episodes straight."

All of which is true but ignores the huge time differentials between events, sometimes in episodes during which, if their life is anything like mine, an understanding of how human life is maintained can change fundamentally.  Or the other, cleverer defence I'm going to think of and get back to you with.  If I remember.