"Hard work" makes no sense as a cause of success. "Hard work" doesn't cause anything, rather, it is a means to an end.

We could contrive an example whereby "working hard" allowed you to "create more widgets in less time than anyone else" and so you receive a promotion (success). But even then we know that your success isn't from just "working hard", but is instead from the result of doing so. Given the context of this thread, I think we can agree that "creating the most widgets in the least time" can be done without "working hard".

I would argue pointing to "hard work" as a cause of success is confusing how a causal factor was reached with the factor itself.