The phrase this time is: protect the priceless key.
I also thought of some other questions to ask yourself about what you’re writing.
Does the material it’s made of tell you anything about it?
I thought of how the flying keys in Harry Potter are not only keys needed to continue on the current quest, but their ability to fly represents an extra challenge. (And that scene reminds you of why this kid was chosen to be Gryffindor’s Seeker: as the key darts, he follows it as he follows the Golden Snitch.)
Also, a key’s material may be unremarkable on purpose. If this is a priceless key, does it look like it or does it look like everybody’s house keys?
Who has it right now? and How is it protected?
Does a protagonist have it? Is it the villain? Is it hidden in a block of amber in an ancient snowy forest? What challenge does the current holder pose to the heroes, if any?
Why is it priceless? and Why does it need protecting?
Is it just a jeweled key that the family matriarch inherited from her grandmother? Is it something that marks you as a chosen one for a quest? Is it both key and amulet at the same time? Is it somehow intensely mundane, but paradoxically fascinating…so you just have to know the story (and losing the key means you’ll never get your answers)?
What does it unlock? and (the question I should have maybe included in the image) What happens when it unlocks the thing it unlocks?
Is it a key to a utopia or a dystopia? Does it merely unlock power, and thus it can’t fall in evil hands lest an apocalypse happen?