Your mother is considering opening a restaurant. Renting the shop is estimated to cost her $80,000 per year and she also needs to put another $50,000 on other expenses. In addition, she also needs to quit her current job as an accountant which earns her $110,000 per year. If your mom thinks the expected revenue is $250,000 per year, should she open the restaurant if she is rational? Explain your answer with reference to the most relevant principle of economics.