Attention is not a productivity resource. It is the medium through which every other capacity you possess is expressed.
Letters 2, 56, and 72 build this argument from three directions. Letter 2 establishes that scattered consumption produces no compounding return — nothing digested deeply enough to change behavior. Letter 56 demonstrates that external noise is not the primary attention threat — internal restlessness is. Letter 72 makes the structural argument explicit: genuine progress requires sustained concentration, and sustained concentration requires the deliberate refusal of inputs that fragment it.