Opinions needed: first impressions

At first, I was like, that's a weird looking loaf of raisin bread.
I'll come back to the freaky bread in a minute. It ties in to my point for the day.

For me, one of the greatest payoffs for investing time in a novel or series is when there's a discovery in character. Like when you find out Mr. Rogers isn't just a nice old man in a cardigan (Ok, maybe he is . . .bad example). But, think of Snape. Not such a bad guy. Or Noah (The Unbecoming of Mara Dyer. If you haven't read this yet, drop what you're doing and get to it.)
Of course this isn't something new. Writers have been doing it for ages, creating red herrings to lead the MC (and the reader) astray.

Now back to the bread. If you haven't stared at the picture long enough to figure out why it looks freaky, try again. What do you see now?

It's not a loaf of raisin bread at all. It's a pug (dog).

The point is, first impressions can and sometimes should give false impressions. (Like the bread dog).
As a writer, I do this often. I lead my main character astray by allowing her to believe other characters follow hard and fast rules. When really they don't.

Question of the Day: How often do you use red-herrings. Or characters that are like the bread-dog? When do you reveal their true identity?