I had a friend email me with a cool question: How do you let the reader in on something the first person protagonist doesn’t?
I know it’s tricky, and I know it can be done, and I know it’s a rush when you pull it off. My answer involved set-up: You establish the character as someone who is liable to miss drawing the correct conclusion when certain types of facts are in front of him, then you can have him report on things from which the reader will draw the correct conclusion, but the protagonist won’t. For example, he might reminisce about a time a certain woman was attracted to him, and talk about the way she communicated it, and then say that he didn’t realize that until much later. Now you can have his current lover drop clues that she is on the edge of breaking up with him, and the reader will believe that he doesn’t see it. If you do it well enough, that is: it’s all about walking the line between, on the one hand, making the clues so subtle the reader doesn’t catch on, and, on the other, making the clues so obvious the reader won’t believe the protagonist doesn’t get it.
Anyway, I thought it was an interesting question, and worth throwing out to the Smart People who hang out here to see what other answers emerge.