Some kitties have a hard time using a scratching post for the first time.
One thing I've noticed is that a lot of scratching posts sold in stores are covered with a shaggy carpet. When we made out own cat tree, we approached it from a cat's point of view. Well, cat claws periodically shed their outer surface, taking with it the sharp tip of the claw. What this does is replace the possibly worn tip with a new, sharp tip. Cats are genetically programmed to find a rough surface, like a tree or rock, and work their claws over it to help shed the old surfaces of the claws.