When a film, book or any other form of media is described, it can sound like it will be a definite winner, and you can't wait to see it. But sometimes when you mix peanut butter and jelly together, it falls short of the experience of a PB&J sandwich.
One example is the film "Wolf" - Jack Nicholson as a werewolf. Jack hamming it up in his own wildman style with no boundaries. That sounds like a natural mix that was a long time coming. But did it deliver?
This trope is not about a failure to execute, but a failure of the pitch itself not providing the 'zing' it appeared to promise.