For your own purposes, as opposed to simply passing the exam, you need to work out which bits of air law
(1) you need to know to stay alive
(2) you need to know to avoid seriously expensive prosecution
(3) are irrelevant twaddle that you can forget the day after the exam.
So very true. And in fact, the bits under (1) can usually be reasonably and easily explained and rationalised, (2) less so, and (3) are usually just a memory exercise anyway.