You know those puzzles you get on the back of cereal packets, where there's a big spaghetti-mess of lines, and you have to help the monkey by finding which line leads to the banana?

Up to a certain level of complexity I can usually look at one of those once, and immediately identify the appropriate line. Bad logic feels like being presented with one of those puzzles, only there is somehow no route to the banana. I can tell, on sight, that there's no route to the banana. There's some sort of holistic wrongness about the puzzle, and it really distresses me that the monkey can't get to the banana!