Hard work is a universally recognized pre-requisite for success in any endeavor incl. Language Learning. Thomas A. Edison once said: "There is no substitute for hard work!" :)

My rough guess: Natural ability: 17.8% Hard work: 70.3% Unknown 11.9% Seriously, hard work counts more than any other factor.

Depends on the language and your own circumstances. First if you (an English-speaker) are learning German or Swedish, it will be easier than Portuguese or French. Also If you are working and don't have much free time, natural ability will let you learn more.

All people have different types of Natural Abilities in different quantities. Different sets of Natural Abilities for different areas like maths, art, language, literature, etc. There are a set of Natural Abilities which really help/influence language learning. Language is a process of translating ideas into sentences (spoken / written) and vice versa. So these Natural Abilities help us to do this translation. The magnitude of Natural Abilities also varies from person to person. But most people have sufficient the Natural Abilities in sufficient quantities. ( a few have insufficient Natural Abilities and some have have Natural Abilities in incredible magnitude) Only Natural Abilities wont make a person proficient in a particular language. The person need some work ( learning, practice,training, etc) But there is a relationship between Natural Abilities and Hard Work. Natural Abilities makes learning easier. That is , the easiness of learning is directly proportional to magnitude of Natural Abilities the person has. In short, more natural ability means less hard work and less natural ability means more hard work. i think this is how Natural Ability and Hard Work are connected. But in practical situations, natural ability would be more useful. It will help us to use the language more effectively in practical situations. All can learn about theories of music. Both, those having incredible abilities and those without much abilities can score full marks in theories. But in practice, those with less abilities will be far far behind those blessed with natural abilities. Regarding handwork: We can reach the same destination through 100s of different ways. But all these ways are not equally easier. So, one must chose the best way for himself/herself. Because other ways will force him/her to take more efforts. But one need not get disappointed for not being blessed by more natural abilities. Because he/she can achieve the same goal through more hard work.

Hard work and motivation are the fundamentals of course. However it takes more than sheer hard work to master a foreign language. And I assume that s all ''natural ability'' is about.