This is an absolutely essential myth of materialistic civilizations. In civilizations where this myth does not exist, the factors that lead to elevated positions tend can be more arbitrary, and sometimes more destructive.
I would say that this myth has been replaced in South Africa by the myth that a person who is a member of a particular party can ride the gravy train until death. It has been such a powerful myth that, evidently, over the last several years more than 700 party officials have suffered untimely deaths to prepare room for aspiring ones, according to a recent article in The Economist.
The verity of the idea that hard work makes success is just good enough to make it widely convincing. When people who are very bright, very well educated, very determined, and very skilled at making connections and using them to advance their agendas, then hard work and luck conspire to create a measure of success.
Remove one or two of these factors and things get a lot more iffy.
A person studying causation would discover that some people succeed without trying very hard. Some people work hard and succeed. Some people work hard and fail. My guess is that there is some correlation between hard work and success; but it is certainly neither a necessary condition of success nor a sufficient one. Believing that it is, however, is necessary for a functional society. And this is why it matters that people at all economic levels benefit materially from their efforts. Failure to do so kills the myth. And then darker forces take over.