Well, the thing is, they did have the right key all along but didn't understand it properly, and so they grew to mistrust it and become sad. The problem was that only by understanding why the wrong keys were wrong, would the right one slide in and open the box!
There was a girl called Hattie who loved puzzles and knew the right key by instinct and this is what she did.
She learnt about all the wrong keys - being scarred and burnt. Her journey was painful and she almost broke, but at the end she knew that unless the others understood the wrong ones fully they could never be free. The key wasn't even to the treasure box they all wanted, it was to the chains around their own hearts. It almost broke Hattie again once she could see them, no longer invisible, each heart was bursting against chains and blaming everyone else for the pain.
She described the wrong ones as best she could:
There were others too, she wrote about them all, then when she turned back to the right key and described it:
The key melted into her soul and all her hurts were healed. The scars were still there and she welcomed them like footprints in sand, evidence of a journey, one to her "happy ever after."