Hardworking is to enrich your boss. I think this idea is only true when you go to work for others, But if you do business for yourself, I think diligence is essential. About Intelligence, In my opinion, Do whatever you need to have the best analysis of the market, so if you are smart you will analyze the market more accurately, helping you minimize risk. Being smart and hardworking will help you succeed in your job.
In my opinion, hard working and the potential negative effects of it can be found everywhere. With wage labor, however, it becomes clear and evident without further explanation, kind of obvious. But it doesn't mean that if you are working hard for yourself only, you will fare much better. The point is when you work for the boss, it is your boss who takes the smart work from you and does it himself. But when you are your own boss, then you have to work smart by default if you want to stay in the business.