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Basic Trope: A dumb character usually not taken seriously actually brings up an excellent point to the astonishment of other characters.
Straight: Ben is usually slow to realize things that ought to be obvious and consistently makes foolish statements. However, in a moment of sharpness, even he finds what Dan is going to do so stupid he can present a really compelling reason for Dan to change his course of action.
Exaggerated: Ben only passed the comprehensive school by the virtue of his impatient father bribing a headmaster, has no social intelligence whatsoever, does and says the stupidest of things over and over again even after he's been told several times in a perfectly clear fashion not to repeat them and so on. However, in an extremely rare moment of lucidity, he presents at least ten compelling arguments for why what Dan is going to do would be stupid and better alternatives with solid justifications, to the point of philosophizing and stealing everyone's breath.
Downplayed: Although Ben wasn't certainly dumb, he was rather lazy in his international politics study, and didn't get a very good mark as his friends did. One day, one of Ben's friend, Dan, suggested a solution for a diplomatic incident, only for Ben to disagree, and with justifications and alternate solutions, which turned out to be completely valid. This was to the surprise of everyone else, as they least expected the party animal Ben to have such insight.
Ben has secretly been becoming more intelligent. Others only haven't seen a glimpse of it until that moment.
Ben is under an influence of something that actually momentarily or permanently increased his intelligence.
Dan is in such a great emotional strain he can't think rationally. This prompts Ben, who has had some semblance of intelligence all along, to metaphorically glance at the mirror, making the moment his starting point of change.
Inverted: Dan is usually incredibly intelligent, both in academic, logical and philosophical as well as emotional and social regard. However, at one moment, he says something so incredibly stupid everyone is mortified.
Subverted: Ben is simply parroting what he heard earlier from Dan's friend Emmett, not actually understanding the content.
Double Subverted: When someone calls Ben out on this, he simply keeps going on - making his own convincing, heartfelt arguments.
Parodied: The team pet, Oscar the dog, gets so annoyed with the stupid suggestions his team mates make he breaks the fourth wall to complain to the author, and makes a good suggestion of his own.
Zig Zagged: The dumb Ben presents a sensible point, but it's simply him regurgitating what he heard earlier. However, he follows up on it with convincing arguments of his own - admitting soon he actually has had no idea at all what he's been talking about - then someone smarter states he still had a point to take note of and backs it up with stronger arguments.
Averted: Ben is none the wiser and never gets any flashes of insight.
"The viewers aren't watching the show because they find Ben overly-moronic. We need to show that he's capable of being intelligent to stop them from being alienated."