not so dumb after all

My answer to a Redditor who asked, how do I write a character who’s uninformed, but not stupid?

Don't think of it as "how can I show this guy isn't stupid?" so much as "how can I show this guy is SMART?".

What would a smart character do when he discovers he's been making a mistake?

He'd never make that mistake again. In fact, he might even stop another character from making that same mistake. Or better still, stop another character from making a mistake which is similar but not exactly the same thing— an action that makes readers, too, go "ah!".

What does a smart character do when he learns a piece of information that, despite being old stuff to other characters, is new to him?

A smart character doesn't just add a bit of lore to his mind stash and leave it at that. He uses that information later in the story, in an insightful way, so as to surprise and delight readers.

When a smart character comes to some new realization about his circumstances, he doesn't simply make an observation about it. He generalizes this information and applies it to another situation. "Ah! It seems that in this world XYZ applies. Well then— doesn't that mean ABC?". And this thought answers some question that's been nagging at readers.

See what I mean? The uninformed, but smart, character isn't just not-stupid. He (or she, obviously, but yours is a he) is a vehicle by which the readers themselves feel as though they are uninformed but smart, and learning quickly how to negotiate your storyworld.