What? I ride horses, and this makes not one bit of sense to me. Remember, what do you do when you fall off the horse? You get back on the horse! Maybe I misinterpreted this poem.

That's the intended meaning. when you fall off a horse, you get right back on because otherwise you'll never get back on- you'll be too scared to. And everyone says it like it's a simple thing to do- just hop back on and it will be like you never had a bad fall, but if the fall off is really traumatic, it's not that easy to jump back up then you're scared of horses, (meant here to be a metaphore for a relationship) for good. Thanks for your comment!