A horse has fallen down on the green grass and the jockey riding on top is trying his hardest to not fall off.
The horse tripped on a rock.
Not necessarily tripped over a rock.
Just because the horse has fallen does not mean he tripped on a rock.
Just because a horse has fallen down on the green grass and the jockey riding on top is trying his hardest to not fall off does not mean it tripped on a rock.