One of the things I did wrong in my first novel was that Lizzie, my MC, was always right. She found the true meaning of every clue right away. This does not make for a good story. It makes for an okay story, but it would have been better (and will be, when I pull that manuscript from the dungeon again) if she'd misinterpreted a clue or two, or only realized half of what it meant.
Why? you ask? Because my friends, that makes for plot twists of awesome.
Think about it. You're reading along, what the MC says makes sense, and then KABLOOIE, the condemning footprint couldn't have belonged to the postman, or the dead guys isn't really dead, or that chandlery isn't just a cover for a bad guy on the run - it's a smuggling ring too, or the man who everyone thought was the father of the illegitimate son is actually covering for the real father, or the MC has two potential villains to follow, and she picks the wrong one.
Or, you're reading along, what the MC makes sense, and what do you know? She's right. She's so clever. She followed the right guy, and fit every clue together perfectly, and thanks to her, the bad guys will rot in jail for eternity.
Which is more fun to read? The first.
Readers like being proved wrong (as long as the new explanation makes sense). Or they like figuring out the true meaning of the clues before the MC, and being proved right. Either way, proving the MC wrong will throw him/her for a loop, and make the story that much more interesting.
As a side note, characters with secrets are an excellent way to prove the MC wrong. Henry lied, and the MC believed him, or Agnes told the MC the truth, and he/she didn't believe her. The MC builds an idea around what s/he believes, and then POP goes that idea, and in the soap suds of its death, a new idea is born, and this one is one step closer to the truth.
What do you think? Feel free to debate and expound upon this idea. I'd love to hear your input.
And a good night/day/afternoon/morning/whatever to you.