Dumbledore hid the stone in the mirror, that was his part in protecting it from harm. he put a spell/charm on the stone, so that only someone who wanted the stone but not for their own gain could see it in the mirror and obtain it.

Harry wanted the stone so Quriell/Voldemort couldn't have it and become immortal, he wanted the stone to be safe. That is why it appeared in his pocket. Harry passed the requirments of the spell/charm that Dumbledore put on the mirror.

Ron never stopped wanting to be a Quiddicth start or Prefect/Head Boy. He did give up and get discouraged but it was beacuse of nerves. He worries that he will not be as good as his brother. Ron wants more than anything to be as good as his brothers are at school, Quidditch, life and to recongize for his accomplishments. That is what motivates Ron even when he doesn't realize it. That is also why he wanted to pass his appration test on his first try because all of his brother's did. Ron's nevers and self-doubt are his own worse eniemes. He is actually very smart and a good quiddicth player.

Harry still wants to be with his parents. He wants to be with Sirius and now Dumbledore. He deals with it better as he gets older. But that desire is still there. He has never had a family of his own (Ron's family is a close 2nd but they are not his blood relatives) and that is what he wants more than anything. Harry wants to be with his blood family, feel their love and have wonderful times with them. This will never happen. That is why Dumbeldore moved the mirror in the 1st place. So Harry wouldn't waste his life wishing for what could have been and not living the life that is waiting for him.