Whether it was a trailer, plot synopsis or promotional image that did it, we've all come across that one movie that makes us drop everything, gaze blankly into space and think "that idea is genuinely 'effing brilliant".
Unfortunately, a good idea is just that; a good idea. Movies are tough to make and sometimes, even the most golden premise in the entire world can be executed with all the style, flair and confidence of a four-year-old child let loose with a crayon. In a plain white room.
Or, to put it another way, a brilliant concept can easily be turned into a complete mess of a movie.
Sometimes, that great concept can disappear altogether under a garbage pile of terrible acting, shoddy special effects and awful dialogue, with everything else around that great hook making you forget that the movie had limitless potential.
There are plenty of examples here, and in many cases, you may have forgot that that movie you hate with a burning passion could have turned out very differently if the quality of the execution matched the quality of the premise.