I once wrote a brief post about how to (not) write smart characters. (Or you can check out Maggie Stiefvater's much more eloquent post that basically states the same thing.)
Today, I had one more realization about smart characters:
Sometimes a smart character doesn't always think of the smartest plan. Sometimes they think of something convoluted and risky, while ignoring the fact that the best plan is actually very simple and almost obvious. (This tends to be the case with a lot of "smart" villains, actually.) And sometimes that's okay, especially in high pressure situations. When you're under pressure, it's very easy to make mistakes.
So is that my realization? That smart characters aren't always smart?
My realization is this: The smartest characters are the ones who have a backup plan.