I've wondered for a long time whether being hardworking is a "talent" that some people naturally have more of. Self-control being heritable would be some support for that idea.
I always thought it erroneous when people say somebody "has the genes to be a great X" but made nothing of it. The ability to actualize those genes, itself, requires good genes for "executing" (motivation, discipline etc..). So if somebody is lazy, but with "great genes", then those genes are in fact not great.
I think the idea many people have is that being hardworking is something you decide on your own and not related to your genes. Being lazy is seen as a character flaw that a person could change rather than something more innate. I think they're right to a degree, but I'm also guessing that it's easier for some people to not be lazy than others.
But if you factor in environmental influence, such as having a tiger parent, then the great genes for X would still be activated without requiring the complimentary execution genes. Nurture nurtures nature.
No doubt, like all things genes, environment has a non-negligible impact.
Have you heard of "learned industriousness"?
I had not heard of the term, but the ideas behind it are what I've considered. My own guess is that it's a mix of both genes and behavior. If being hardworking was based purely on the environment then I suspect that we would see a lot more success in treatment of ADHD without drugs. But it does make intuitive sense to me that it is something you can build up as well.