Don't panic. I'm not going all-out academic on you. Today's post is simply about the quirks of the American English language (as opposed to British). More to the point: what is said vs. what is meant.

When I say:
Wow, that garbage can is full.
It means:
Get off your butt and lug out that Hefty bag, would ya?

When my husband says:
Can I help with dinner?
It means:
Have you been on Pinterest all day or what? Why isn't the food on the table yet?

When the sales clerk says:
Have a nice day.
It means:
I don't care a rat's behind what kind of day you have as long as you fill out the survey on the bottom of the receipt and make me look good.

When words are spoken face to face, it's easier to decipher because of body language. But when the written word is your medium of choice, it's all the harder to convey what a character actually means. On the up side, this can be used to an author's advantage by choosing words that convey characterization via dialogue.

Or it can leave your reader scratching their head with your book firmly shut on the nightstand beside them.

What to do?

The best way to make each of your character's say what they really mean (and not give the reader a different expectation) is to really know your character well before they even speak. This requires some groundwork before you begin a new manuscript. Yes, this takes time, but in the long run it will pay off.

Know your characters. Know them well. Then use the words that flow out of their mouths to solidify who they are in your reader's mind. Those are the kind of characters that stick with a reader long after they've closed the book...and not just left it to rot on a bedside table but given that book a place of honor on their living room shelves.