just beat computer, level 6 for the first time, and discovered that one of the many tactics that I am not getting is middle game pinning. many times throughout the game I was in a position where I wondered why the computer wasn't taking a piece that was just sitting there, waiting to be captured. Then I realized that I had the attacking piece in an absolute pin. It must take years to get to the point to see this on a regular basis, and to actually get there on purpose! lol