If your protagonist is proud of her intelligence, she may very well propose a clever solution to a problem, and then be astonished when she tries to apply that solution and it doesn’t work because of other forces she figured to take into account.
Because of other forces she forgot to take into account, maybe? I guess I'm particularly sensitive to this since it's my favorie kind of mistake and the one I most frequently inflict on my protagonists just for the sheer fun of it (and because it's the one I can identify with most easily). On the other hand....
But I appreciate that a protagonist who does so can look awfully stupid.
Sometimes stupid protagonists can be fun to read and write about, especially if the stupidity is intentional. The first chapter of The Three Musketeers wouldn't have been so funny if it wasn't for D'Artagnan's stupidity. Guybrush Threeplock (?) in the Monkey Island games is so adorable because he's a little stupid. And I suspect Naruto is so popular among the fans of Japanese comics and animation because it breaks the recent trend for dark, brooding protagonists by returning to the older theme of a brave, talented, loyal, and dedicated but rather stupid hero (the eponymous Naruto).
Maybe you could write a rant on stupid characters? Or on making an important character's stupidity look intentional rather than being an udnesirable side efect of an Idiot Plot (TM)?
Oh, BTW, maybe you'd be interested to write a polemic I wrote some time ago on the inventiveness of brilliant generals (http://l-clausewitz.livejournal.com/312198.html)--just for fun if nothing else.
Guybrush Threeplock (?)