Stubborn or persistence?

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Hi friends in Mylot, it has been several months since my last logging in. Actually, I'm occupied in preparation of the national post graduate entrance examination, which will begin in January next year. It's really important to me just like the GMAT to Americans. I see it as a turning point of my life if I succeed passing it. Therefore, I pay almost all my efforts preparing for it but thus I have to quit many specialized courses, which lands me on a edge of the failure of the final examination, though it may not affect direct the post graduate entrance examinaion, it means that I will lose my scholarships I have won for several times. My roomates have told me that it's not worthwhile to quit so much for the examination, I have to consider the possible failure. However, I really value it and know what persistence imply for the success. But sometimes, someone can say it's stubborn. I don't know whether I'm stubborn or not and what's the distinction between stubborn and persistence. Is it worthwhile doing it in such a way?