If you ever need to be reminded just how much the impact a story can have on an audience, just watch a child as they read/watch/hear a plot twist for the first time. The combination of joy, shock, and wonder that spreads across their face is a wonder to behold.
And if you don't happen to have any children handy, you'll be happy to know that YouTube has done your work for you. A great example is here, and you can see a whole compilation of kid reaction shots here. (All of these are showing reactions to a particular reveal in The Empire Strikes Back.)
Adults have this same reaction, though sometimes we bury it under a layer of cool detachment. It may vary, both with the length of the tale and the skill with which it's told, but at heart, we're all the little kids gasping with awe when we hear a powerful plot twist.
Barrie Hardymon's recent piece on the NPR Monkey-See blog is about reading the Star Wars novelizations to her son, but it's also a meditation on the power of story and the great responsibility (and joy) that comes with being a story-teller.
Whether you're writing a short story, a biography, or advertising copy, remember the power of the surprising twist, and you'll stir interest and emotions in your audience.
(warning: the NPR story contains spoilers for Star Wars, Jane Eyre, Harry Potter, and several other stories from the 19th & 20th centuries.)