---> this is the face you make when your readers are all "Um, I know you want me to think the Butler did it, but I know how to spot a red herring when I see one. Busted"
Let's talk about "The Man Behind The Curtain Syndrome." I'm assuming you all remember the iconic scene in THE WIZARD OF OZ (the original) where Dorothy and her gang of broken heroes discover the Great and Powerful Wizard is not a fearsome apparition, but rather, a sheepish little white haired man in that suit that makes him look like a fancy garden gnome. The mysticism and awe is gone. The belief in the (other) worldliness of the wizard, the conviction surrounding his myth and legend... poof . vanished.
The same thing happens when a reader can feel you, yes you, the author, pulling the proverbial strings of your novel. When we - your humble readers - feel you manipulating us from behind the veil you've penned, we're kicked right out of the story. The sense of immersion and fluidity is gone. We can see your shoes sticking out from under there!
So, how do you know if you're committing the sin of curtain-dom? And, harder, how do you fix it? There's no formula, but here are some tips:
1.) the super obvious clue - so you wrote the scene where you placed the first clue. You left that teensy trail of breadcrumbs. But you've got this nagging sense that the reader might not see it. Maybe you should make it just a little clearer? Maybe you should up-end a bag of Doritos instead of that trail of crumbs, yeah? DO NOT DO THAT. Reading is an exercise in faith; you must trust your reader to follow your bread crumbs. And it's much easier, I think, to edit the clarity into project than to edit the obtuse out of it.
2.) the bright, neon red herring - I will caveat this by saying that one of my favorite things ever is when I think I'm hot s**t, and I'm all "oh duh, that's totally a red herring and it's clearly Bobby who killed him" and then I find out I am totally wrong and it turns out Bobby's little sister is a rampaging murdering psycho. It's kind of a double-fake, so if you're working on that. Brava! But if you're building a basic red-herring, make sure you're not putting a spotlight on it. Ask yourself if it works in the story organically or if you forced it in there? If you're forcing it in there, chances are your reader will spot it.
3.) Symbolism - C.S. Lewis is a master. I adored the Chronicles of Narnia. But, I have to admit, re-reading them when I was older was an exercise in patience, because OMG I GET IT AZLAN IS JESUS. Can we actually get back to the story now? the point: Symbolism=good. Bludgeoning to death by allegory = Bad.
4.) Like me, Like me, Like me! - look how funny, smart, perfect, snarky, goofy, pleasant, polite, gothic [insert adjective here] I am! This one doesn't happen too often, but every once in a blue moon I come across a protagonist who reminds of someone trying too hard. Unless your MC is a sycophant, you just really want me to get invested. It's alright. Relax. You don't have to lay it on so thick. Worry about your MC, not about me. Not yet, anyway.
5.) This is how kids talk, right? - this is, I think, the most rampant cause of "man behind the curtain" syndrome, and also the most difficult to fix. When your MG protagonist sounds the way adults think kids sounds, feel like I'm being condescended to (and you can bet a Middle Grade editor would, too). It's the feeling you get when parents try to use slang. I'm still not sure how this one happens, but I think it's from concentrating too much on the words; on getting the style right, and not enough worrying about your characters.