One problem I face as a mystery writer (and reader) is how smart the protagonist gets to be. Even when I was a kid I knew that Sherlock Holmes was often way off in his self-proclaimed "logical deductions". Saying that a man's wife no longer loves him because his coat has a loose button is beyond ridiculous, and such Holmes moments have been spoofed many times by comedians better at it than I.
But here's the thing with mysteries: writers have to make leaps sometimes to make the story work. The cop has to have a gut instinct that tells him he's on the right track, so he zeroes in on one suspect out of the twenty possibles. The detective has to be better than everyone else at putting the pieces together and finding a solution, so she sees the connection between victims that everyone else has missed all these months. The amateur sleuth has to make a leap from "it could be anyone" to "what about this guy?" , picking up on some small detail that sets him on his often bumbling path to the story's climax.
The author's job is to make these moments palatable for the reader, so everyone goes along, takes the jump, and makes it to the other side. It's one of the mystery writer's most difficult tasks: if the gap's too big, the reader can't or won't span it. If it's too small, the reader's way ahead and eventually wanders off to look for something more interesting. And if your crucial clue is that the dog didn't bark, well, good luck with that.