Jeffro, writing on misdirection and how that doesn't just apply to mysteries, brought up this:
If you ever notice something along the lines of a “Chekov’s Gun”, then you know the spell has not been successfully cast. In David Brin’s first book Sundiver, there is sort of a brain dump at some point. I get to it and I think, “why is he even talking about this stuff?!” And then I get to the end and I realize that he had to tell me that stuff so that I would understand what was happening at the ending.
I get that same feeling frequently when I watch movies. It’s like Bill Cosby’s classic set up for (I think) his Fat Albert story: “Now… I told you that one so I could tell you this one.” That got a laugh in his stand-up routine. If people notice you doing that when you’re telling a story, then you are failing to successfully misdirect your audience. You’re like a magician doing a trick and instead of wowing the twelve-year-old on the front row, you instead draw attention to the dime store gimmick that makes what you’re doing possible.
It’s bad form.
For what it's worth, if you can sense a shift in the story, as if an entirely new story is being told for which this was the setup, maybe you have two stories.
That said, I've seen this pulled off, masterfully, once.
Anathem, by Neal Stephenson. Roughly halfway through the book I wondered why so much time was spent on Erasmas and life in the concent. Sure, it had some interesting discussions on philosophy, bud dammit, not much was moving along!
I actually thought of that Cosby joke.
By the time the book wrapped up, I realized that without the beginning, even if the initial revelations that triggered the events of teh second half were pushed back, the book would not made sense. The characters needed that room to grow, developments needed to work in sequence, and room needed to be made to slip one piece of background thought in at a time to understand the how and why of the end without huge infodumps. Or even bigger ones.
For a story that halfway through started feeling like two, it ended up starting no later than it possibly could have.
As to that Cosby joke:
Also, one commenter asked if Jeffro's take on Sherlock was referring to the Christmas special. While I cannot speak for Jeffro, my personal answer is no.
I mostly enjoyed the first season, somewhere around two it started to bore me. The final? I knew it would be a total train wreck from the first episode, even leaving aside the horrible posturing of the Christmas special and it's oh-so-obvious politically correct mystery.
For those who are gluttons for punishment, and want a red-letter-media level of detail in why it sucked (without the psychopath serial killer jokes):
Keep in mind that, from several comments, the reviewer actually approves of progressive "checkbox" grandstanding.