The world is littered with the tales of small businesses in the dire straits of hiring that spent time and money they couldn't afford to hire people who couldn't perform.
No matter what your company does - build, manage, produce, import - as an owner, you can't avoid the hard work and skip straight to success. No class can give you that, no YouTube video can teach it, and no book can mark it off your list.
Certainly, the human race can be fickle, and times do change, but overall, the barriers to bringing a product to market - and understanding what 'the market' wants - have remained unchanged.
Without concentration, a business will be ordinary in every respect, because it will have no presence, no inner force, no way to attract the people upon whom it depends for its very existence - employees, customers, suppliers, and lenders.
If you are with five successful people, then you are the sixth successful person. The reverse of this is true as well, so who are you hanging out with?
Small business owners and entrepreneurs worthy of the title need to build systems that replace themselves.