In the past some of the most professional entrepreneurs were people who worked as doctors, or accountant,s or lawyers, or engineers. To get to that level in these professions these entrepreneurs had to sacrifice a tremendous amount of time and money early in their career.
This included the amount of time spent going to college as well as building a clientele. Once they opened up their own business it also meant they were possibly deeply in debt and spent much of their early careers repaying things like college loans.