That is a quote from one of my clients. He and a partner own a very successful manufacturer. As you might imagine, there are many issues: sales and marketing, finance, employee relations, engineering, OSHA and EPA compliance, etc. All are important, and if not done right, can cause immense problems in any business. But he said “I do the purchasing”. That is the critical core function that if not done right causes more than just problems, it causes failure. He had picked out and is personally in charge of the mission critical piece of his business.
The owner of another client, also a manufacturer, approves all capital expenditures. Not just the big ones, all of them. That is the cash flow critical piece of his business. Large or small capital expenses for unneeded or overpriced equipment could break him. So, he personally handles that.
Another client handles all employee recruiting. Personally. Her business is to provide professional nursing services on long term contracts to manufacturers throughout the US. Her mission critical work is to make sure the nurses meet her standards. So she hires all of them. Personally.
One more. A long time friend of mine who manages fixed income securities for clients all over the world said to me he does 2 things (ok so it is more than one, but you get the point): “I work with my clients and I decide what we buy and sell.” All of the rest: compliance, data processing, employee relations, reporting, etc., is managed by others.
Indeed, non core functions need to be well handled. But the successful entrepreneurs know their critical core functions, and that is where they focus their energies. It works.