There's your candidate. You already know the person and trust him or her. People committed to a business are often interested in becoming the owner, but not always. If you have no employee like this, it may be time to start looking for someone to bring into the business. Many young people would welcome coming into a job that offers the opportunity of advancement.
Some sole proprietorships sell very personal goods or services.
They are your babies and they can't expand. But this is extremely rare. But if you think you are one of them, think again. Let's say you are an actor. Sure you get roles based solely on your own look and acting ability.