Good point, but on the other hand, if you're already in control of yourself, how can you gain more control?
This could get weird if we don't define our terms. If your "self" is your mind/attention, then sigzero is right by saying complete control is impossible; the human mind is too whimsical to ever be fully reined in. But we can consciously course-correct...
Self could be your mind/attention, but there's no reason you can't expand your idea of self to include your ego, mind, entire body. I suppose the question is: will you take responsibility for what goes on within your skin?