SAT essays, off-topic or not?

I’m really confused about how do graders grade essays. In the March SAT exam, my topic was “Does using self-discipline take the joy out of life?”. I said that self-discipline took joy out of life but those who do this change the world and used Galileo and Kepler as examples. I did mention that they didn’t enjoy their life because of self-discipline, but I was actually arguing “self-discipline changes world”. I thought this would be off-topic, but surprisingly I got an 10. I’m going to take this weekend’s SAT and is really concerned about this issue. Say, the topic is “Is imitation of others always harmful?” and I argue those who succeed are those who are original in their own ways, would it be off-topic? By what standard is an essay off-topic? I

See: http://abcnews.go.com/GMA/ConsumerNews/teen-student-finds-longer-sat-essay-equals-score/story?id=12061494