There's another problem that often appears in retelling an old story. It fades like an overexposed photograph, or a copy of a copy that gradually loses detail and color. If your adaptation is less powerful than the original-- if it doesn't have that same twist of horror or joy that makes a reader catch their breath-- then something's wrong.
Let's look at another frequently adapted tale: The Ballad of Mulan.
Mulan is an ancient Chinese ballad that tells of a girl whose aged father is drafted into the army. To save his life, Mulan disguises herself as a man and joins the army in his place. It's a tale of courage, and a daughter's deep love for her father.
Here is the original ballad's account of Mulan's decision:
Tsiek tsiek and again tsiek tsiek, Mulan weaves, facing the door. You don't hear the shuttle's sound, You only hear Daughter's sighs. They ask Daughter who's in her heart, They ask Daughter who's on her mind. "No one is on Daughter's heart, No one is on Daughter's mind. Last night I saw the draft posters, The Khan is calling many troops, The army list is in twelve scrolls, On every scroll there's Father's name. Father has no grown-up son, Mulan has no elder brother. I want to buy a saddle and horse, And serve in the army in Father's place."
Probably the most famous adaptation of Mulan is the 1998 film by Disney. Here is the animated version of Mulan's decision, told without dialogue, through music and images. I still get chills when I watch it.
Last, let's look at an example of an adaptation that goes through all the motions of being faithful to the original, but has about as much heart as a well-oiled robot.
Wild Orchid, by Cameron Dokey, is a novelization of Mulan intended for YA readers. Here is Dokey's account of Mulan's decision:
If I had been a son, I could have gone to fight in my father's place. My father could have remained home and our family could still have kept its honor. But I was not a boy; I was a girl. A girl who could ride a horse...A girl who could shoot an arrow from a bow made for a tall, strong man and still hit her target... A girl unlike any other girl in China.
I must not let my father go to fight, I thought. I will not.
...And so I would do the only thing I could to protect both my father's life and our family's honor: I would go to fight in his place. I would prove myself to be my father's child, even if I was a daughter.
Wild Orchid is a decent book. Dokey obviously did a good bit of research. But it reads more like what the author thinks Mulan ought to think, rather than the story of a terrified girl who does the impossible to save her father.
I've forgotten nearly all of Wild Orchid, but I still remember Disney's Mulan, weeping in a thunderstorm. A girl who is small and powerless. A girl who stands up and steals her father's armour.
So when you write an adaptation, stop and ask yourself if you're going through the motions. Are you writing about Mulan, or are you Mulan, hands bleeding, knuckles white, hands clenched around a sword?
If not, shelve it. Lock the story in a drawer and forget about it for a month or a year. Then take it out and try again.