Simply put, your business model is the answer to the question "How do you intend to make money?" It's your plan for how you will generate sufficient revenue to meet your expenses and earn a profit. Unfortunately, many independent professionals don't actually have a profit-making plan. And some of those who think they have one are relying a bit more on magic than they are on statistics.
For example, when you first hang out your professional shingle, charging $100 per hour may seem like quite a lot. After all, if you earned as much as $100,000 per year at your last job working a 40-hour week, you were still only making $48 per hour. So perhaps you think that doubling your former hourly rate should be more than adequate to keep your net earnings at their former level.