The major lesson that I learned from my son Izhak is that of learning in depth, that is with lot's of review until I understand, and even then to keep on reviewing. I had of course been introduced to this at Shar Yashuv and the Mir yeshivot, but the lesson did not really sink in until Izhak explained this to me. But it still seem to me to be unclear how much review to do. I have been thinking of the idea of focusing on one subject and kind of expanding out from there.
Even though Rav Nahman is known for advocating the fast kind of learning, see his book Le.M vol I chap. 74 where learning with iyun [review and depth] is considered to be a higher level.
to rav nahman there are two kinds of judgment: (1) from the realm of holiness, (2) from the realm of uncleaniness. The last is understood: sickness, tragedy, etc. The first i when one tries to come into the realm of holiness and just then troubles begin. These come as tests of faith, or because one was not fit in the first place. And learning without understanding is the same essence as judgment of the realm of holiness. But when one learns with understanding that mitigates and weakens that all the judgments.
