I think the second part of the “and see what happens” theme had a lot to do with that. If I'd just had to break a box, I'd have thought a lot more about the gameplay. But since I had to "see what happens", I ended up thinking a lot about the reasons for breaking a box. All this led me to Pandora's box and, one thing leading to another, to a story.
But that's also why this game took a lot longer than expected to make. In the end, telling a story is much more complex than simply setting up a gameplay.