The Importance of Putting a Stake in the Ground

Mystery is when the author is hiding things from the reader, and intrigue is when the characters are hiding things from each other. How do you deliberately hide things from other characters without doing that coy thing where you're withholding from the reader? Or the other big problem is where you don't let characters talk about things they would normally talk about in order to further the plot. Yeah. You can have both stories.