Do cats always land on their feet?
Yes, if they have enough height to get upright before landing. Science has determined that's about 1 meter, or three feet. As in this video:
This is known as the cat righting reflex. Their flexible spine and virtual lack of collarbone lets cats do it with such speed and ease.
Our Reverend Jim became fond of sleeping on top of a bookcase, five feet off the ground. He would keep putting his back to the edge; and we kept patiently flipping him over, because seeing his back droop further and further over the edge meant he would eventually fall. With the time it would take him to wake up from such a deep sleep, he wouldn't be able to use his ability.
It's more accurate to say that a cat can land on their feet.
But they don't have the superhero power to be unharmed by a drop from any height.