Why do we find reading interesting?

I've been here for almost 2 months now, and I find every FanFiction is interesting.
And from time to time, I react in real life.
I began wondering why I keep doing so, I say so to myself "Because it's interesting!".
So why do we find words transformed to stories 'Interesting'?
It starts when we understand a word, then the sentence.
And you (sometimes) may picture the sentence in your mind, which may have your interests.
Which is us ponies (Or the storyline).
You then think what else there could be farther in the story.
So you read ahead, finishing sentence after sentence, out of curiosity and interest of what is gonna happen next.