The rule of three

Apart from crafting exquisite run-on sentences, finding the rule of three in a piece of writing is probably my favorite pastime—like a free treasure hunt for nerds. It's a simple building block device driven by rhythm, symmetry, and surprise—and once you're aware of it, you start to notice it everywhere. 

In Michelle Obama's speech on Monday:

"How we urged them to ignore those who question their father’s citizenship or faith. How we insist that the hateful language they hear from public figures on TV does not represent the true spirit of this country. How we explain that when someone is cruel or acts like a bully, you don’t stoop to their level."

Here's Roy Peter Clark at Poynter detailing the writing lessons in that speech (which was tremendously well written, and one of the best I've ever seen delivered):

Lesson four: Unleash the power of three. Notice how often the speaker relies upon a pattern of three to make her point. This is one of the oldest tricks in the orator’s book. In literature, three is always the largest number. "Of the people, by the people, for the people." Four examples or 40 become an inventory. Three encompasses the world, creating the illusion we know everything we need to know.

Here's the rationale behind it, from Copyblogger:

It all comes down to the way we humans process information. We have become proficient at pattern recognition by necessity, and three is the smallest number of elements required to create a pattern.

& on its use in comedy:

The Rule of Three fits the classic joke structure of set-up, anticipation, and punchline. The three-part grouping also allows for tension to build and then be released thanks to the surprise and absurdity contained in the third element.

& from SNL circa 2008: Tina Fey and Steve Martin:

Tina Fey: [ smiles ] I think I CAN do it!
[ Steve slaps Tina across the face a second time ]
Tina Fey: What was that one for?
Steve Martin: That one was just for fun!
[ Steve slaps Tina across the face a third time ]
Tina Fey: Was that one for fun, too?
Steve Martin: No, that's the Comedy Rule of Three.

+ bonus: more from Ken Levine, TV Tropes, and Forbes (!)