When you first start to study a field, it seems like you have to memorize a zillion things. You don’t. What you need is to identify the core principles—generally three to twelve of them—that govern the field. The million things you thought you had to memorize are simply various combinations of the core principles.
Reed contrasts the apparent complexity of an unfamiliar subject with the smaller set of ideas that gives it structure. His central point is that learning involves recognising how information fits together, rather than treating every detail as a separate fact to be memorised.
On this view, core principles provide a framework for interpreting examples and solving problems. A learner can ask which principle explains a particular case, how several principles interact and whether the same reasoning applies elsewhere. The emphasis is on understanding relationships, so that new material can be connected to what is already understood.
The suggested range of three to twelve principles is best read as a rule of thumb, not a universal limit. Nor does the argument remove the need to learn facts or practise skills. It proposes using general ideas to organise detailed knowledge rather than replacing that knowledge.