can't speak for other INTjs, but I picture my life before it happens and I must always stick to that plan. So if I imagine that I will graduate, I must pass all my exams first. If I should fail on a huge exam, I will feel like my whole life plan is flawed. If I didn't pass on that exam, that means I will fail in university and then I will never get a good job and then I will never be a scientist and then my life will be awful and I will die poor and unhappy... So suddenly it becomes extremely important for me to pass on that exam. It's totally sick, I know. And I suspect that this is the reason why depression is so common among INTjs.
You sound INTp.
Not really-this is EXACTLY how I feel...The question arises as to whether "greatness" is really worth it.