I’m not sure why, but there’s something about the number three that works very well in writing.
A list of three items – “I love apples, oranges, and pears” – has an effective, easy rhythm that helps us remember the list.
The standard Hollywood screenplay has three acts – Act 1 introduces the hero and sets up the main plot, Act 2 complicates the plot in order to make life hell for the hero, and Act 3 lets the hero defeat the villain, win the girl and live happily every after.
A classic rule of repetition for speeches, sermons and presentations is to say everything three times: tell them what you’re going to tell them (i.e., the preview); tell them (the content); and then tell them what you just told them (the recap).
Finally, the underlying structure of almost any piece of business writing is threefold: intro, body, and close.
So embrace the power of three in your writing. Build a list, give a speech, structure a document.