Allen explains, in rather extreme detail, his methods for attaining productivity without stress. His most effective and persuasive point is that you must get everything ‘out of your head’ and into a system in order to reduce the stress of ‘knowledge work’ (I hate that phrase).
The material is quite dry and could easily have been condensed into a pamphlet without a significant loss of information. After a few chapters of reading I opted for skimming the rest of the way.