Why Three?

Current Theme Song (aka what's playing on my ipod right now): When Can I See You Again by Owl City [Wreck it Ralph soundtrack].

This post is meant to be more of a mind igniter than rhetoric. So simply, comments are welcome, because this is something I am not entirely sure of myself.

Why is the number 3 so powerful?

In fairy tales it holds a strong motif in particular almost to the point of being an archetype. Three wishes. Three impossible tasks. Three kindnesses given in return.

Trilogies in books seem somehow… complete. Two is too few, four is too many (and feels out of balance even though mathematically it is in perfect balance), but three is just right. (catch that fairy tale link?) ;)

Is it because it feels like a story structure? That is has a beginning, middle, and end? Or perhaps it makes it seem like the stakes are much higher that if the protagonist tries, then fails, tries and fails again that is truly is an impossible thing?

I think it has to do with what someone has called The Rule of Three. One is an instance. Two establishes a pattern. Three becomes a rule. A blip from the Wikipedia article linked above:

The rule of three is a writing principle that suggests that things that come in threes are inherently funnier, more satisfying, or more effective than other numbers of things. The reader or audience of this form of text is also more likely to consume information if it is written in groups of threes. From slogans ("Go, fight, win!") to films, many things are structured in threes... One of the best examples of the power of the rule of three is in comedy, where it is also called a comic triple. Two is the smallest number of points needed to establish a pattern, and comedians exploit the way people's minds perceive expected patterns to throw the audience off track (and make them laugh) with the third element.

And it doesn't even have to apply to anything of enormous significance to a story. Subplots and tiny details which work on the subconscious can be extremely effective in this regard.

Like courage in fairy tales, I think these scratch the surface, but are not necessarily the whole picture. So why do you think three is such an important number to us in stories, culturally, and in life?