Just about every magic performance employs an unexpected happening, but remarkably few presentations employ unexpectedness.
Take the Heaven on the Seventh Floor video I mentioned in my Simplicity post. The elevator is shown empty, closed up, and then David Copperfield magically appears inside it. Once the elevator was shown empty, almost everyone who sees this expects a magical appearance. To be fair, this routine gets its memorability, its stickiness, from simplicity, not unexpectedness.
Unexpected presentations are about attention. More specifically, unexpected routines are about getting attention and keeping attention (directing attention is another matter entirely). Getting attention actually requires a different approach than keeping attention, so I'll discuss them one at a time.
I'll start with an example of getting attention right out of the Made To Stick book:
This ad takes advantage of an established pattern, that of standard car ads. It then, jarringly, breaks that pattern. The unforeseen breaking of a pattern would seem to a sufficient definition of the unexpected. But what if a gigantic green monster jumped out in front of the car, picked it up, and swallowed the car and its occupants whole? That would certainly break a pattern and be unforeseen, but that ad would have a much weaker impact.
While the breaking of the pattern can't be foreseeable, it should be a natural outgrowth of what has happened before. In Made To Stick, Chip and Dan Heath coined the word postdictable to describe this concept. A good example of a postdictable idea would be the twist ending of The Sixth Sense. Once you've learned it, you can go back through the movie and see the clues that led up to it.
In contrast, recall the episode of Dallas in which Pam learns her husband Bobby is still alive, despite his being killed earlier in the same season. When it was revealed that the entire season was just a dream, it certainly made that episode memorable, but it also made that episode regarded as one of the most gimmicky in TV history.
As an example of getting attention in magic, view this video of an escape by David Copperfield:
Note that the routine is presented as an escape, with the focus on the dwindling time he has, depicted by the clock and the height of the saw blade. That pattern is then broken, and even highlighted with sparks!
Getting attention is great for a few moments. What about when you need to keep attention for an extended period of time?
Look at any mystery movie or TV show. They have to keep your attention it for up to 1-2 hours! While the twists and turns in the plot are certainly part of the mystery, these unexpected moments aren't what are keeping your attention. At the beginning of the msytery, a gap is created in your knowledge, and this gap isn't fulfilled until the end. You're constantly asking, What will happen? Am I right?
As Darwin Ortiz explains in his book Strong Magic (see section 3b of the Dramatic Structure section of my Questions For Better Magic), the three major ways to do this in magic are to use mystery to evoke curiosity, conflict to evoke uncertainty and tension to evoke anticipation.
One of my favorite examples of keeping attention is a story about whether a lighter will light 10 times in a row. Does that sound boring? Described that way, it certainly is. However, this story starts with a young man bragging to beautiful woman that his lighter never fails to light. A bet with another man ensues as to this claim. The man bets his Cadillac that the younger man's lighter won't light 10 times in a row. As the younger man has nothing of equal value to bet, it is agreed that the young man will bet his little finger. If the young man wins, he gets the Cadillac, and if he loses, he loses his little finger. The lighter then starts lighting. It lights the first time, then the second.
I bet whether that lighter lights up 10 times in a row sounds much more interesting now. What happens? You'll have to read the story The Man From The South to find out!
Naturally, you don't want to read a mystery book, only to find the last few chapters missing. During most magic routines, you have to close the knowledge gap you've created. If you were to, say, bring out a case that occasionally moved by itself, and never revealed what was in the case, you could disappoint your audience, damaging interest in any later routines you perform. Also, just like when getting attention, the revelation must be postdictable!
Notice that I said most magic routines should close the knowledge gap, and that not closing the gap can damage interest in later routines. The closing routine is a special case. If you open up a knowledge gap as the end of your final act, you'll definitely be remembered. The South American magician Richiardi specialized in performing horror-themed magic. He'll always be remembered for how he closed his show:
Notice that this clip gets your attention right away by being narrated by Teller, the normally silent half of Penn & Teller! More importantly, notice the effect that the lack of closure has on the audience. Do you doubt anyone who saw his shows ever forgot him?
I should add that unexpectedness can be overused. If every routine you perform has a surprise ending, or begins by creating the knowledge gap, your audience begins to anticipate the unexpected turns, and the twists begin to lose their effectiveness. I mentioned earlier that Copperfield's Heaven on the Seventh Floor routine didn't employ any unexpected aspects. That doesn't mean its bad or not memorable. That just means that Copperfield was experienced enough to know that he could save unexpected occurences for parts of the show where they would be put to better use.
If you need to command attention, adding an unexpected element to your presentation is the key. For more on the power of the unexpected, check out the unexpectedness category of the Made To Stick blog.
Memorable Magic: Simplicity