He covers all kinds of stuff such as goal setting periodization and what the evidence indicates about exercise intensity is well worth the read if you’re prone to quit training:
Back to the intensity issue. Unfortunately, this is another example of experts prescribing what they think people will do rather than what’s best or optimal. Reviewing the research makes it clear that higher intensity exercise leads to a longer life and less cardiovascular disease. (5) Studies have also demonstrated that people who do higher intensity exercise are leaner than people who only do low or moderate intensity exercise even when they eat more calories and burn fewer calories during exercise. (6) In short, you get more bang for the buck with higher intensity exercise.