I can't say I've seen the semi-colon used quite that way - maybe it's a strong dash instead of a strong comma. I believe your analysis is correct. Why he uses a dash in the P not P case and a comma in the D not D case is beyond me.
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NL888 True discipline achieves a balance by producing-not pushing; of diligence, not driving = True discipline achieves a balance by producing-not pushing; true discipline achieves a balance of diligence, not driving?