Kate Middleton's brother attributes his success to his hard graft. Here.

I don't think so. I mean, for example, is it simply a correlation that his businesses are all party-related or is it because his family is in that line of  business anyway?

He is making the following argument: I work hard so I'm successful. No, not necessarily. It could just as well be I'm successful so I work hard. And that's what it undoubtedly is in this case. Most people would work hard if they had a reasonable chance of success. The reason why so many people don't  is because, for many, hard work will not bring success that is proportional to the work undertaken. James Middleton's education, connections, etc make it almost impossible to fail if he decides to 'work hard'.

James Middleton is lucky. He refuses to admit it. He is is a snob and a braggart.