Threes

I don't know if you've noticed, and I'm not sure when it started, but books seem to always come in threes these days.

Maybe Tolkien was the first with the Lord of the Rings trilogy?

But recently there have been a spate of them - Hunger Games, Twilight, Millennium Trilogy (Girl with the dragon tattoo), His Dark Materials, Fifty shades of Grey (no I haven't read it, no I'm not going to either!).

Maybe someone has done a study and discovered that three is the optimum number to tell a story, maybe it's the most that readers attention spans can cope with?

Whatever it is, it seems all best sellers come in threes - except when it comes to film adaptions, when they often feel the need to split the final book into two films (Twilight and Hunger Games).