Answer:
The operation performance of a business cannot be evaluated through only the revenue it generates as it does not the money that the businessman earns. To simplify it, when starting business, the founder has to invest on the business an amount of money, which is the expense for business establishment and operation. After operating, the business generates the revenue. However, the true earning is only equal to the profit (profit = expense - revenue).
So in the situation of the business owner given, the reason he cannot keep the doors open is because the expense on operating business of him is greater than the revenue ($2000), which makes the profit less 0. So that he cannot actually earn more money but just lose if he continues investing more.
