I think the worst offender here is the History Channel and all their programs on the so-called "World War II"[…] they spend the whole season building up how the Japanese home islands are a fortress, and the Japanese will never surrender, and there's no way to take the Japanese home islands because they're invincible…and then they realize they totally can't have the Americans take the Japanese home islands so they have no way to wrap up the season.
So they invent a completely implausible superweapon that they've never mentioned until now. Apparently the Americans got some scientists together to invent it, only we never heard anything about it because it was "classified". In two years, the scientists manage to invent a weapon a thousand times more powerful than anything anyone's ever seen before – drawing from, of course, ancient mystical texts. Then they use the superweapon, blow up several Japanese cities easily, and the Japanese surrender. Convenient, isn't it?
…and then, in the entire rest of the show, over five or six different big wars, they never use the superweapon again. Seriously.