This November was my sixth 10 day Vipassana course (first was 12 years ago). I achieved momentary clarity on the 8th day which helped me get rid of some of unnecessary but deep rooted complexes of my mind. I believe that it was possible only because of the continued practice and focus of the past 7 days. If it were two courses of 4 days each with some gap in between, I do not think I would be able to experience what I did. In other words, I feel that my brain needed the 10 consecutive days.