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.
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.
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.
Look at what is average in your area, your industry, and your company and then be better. That could be as simple as reading another book each month or attending a seminar each year. On the other hand, it also means acknowledging what 'average' actually is and how you, as the owner, arrive at that figure.