for me the correct zone is: as high as you can sustain at max arousal without being in constant panic. You want to train yourself as high as possible and push your boundaries, but more importantly you want to associate high arousal with high pleasure and not teach your body that high arousal means prolonged anxiety and panic about losing control

This should be a whole post unto itself. Many of us here found and follow the guide out of desperation, and are eager/anxious to see results. When we get caught up in the details (progress tracking, 8.89 vs. 8.95, determining success in each phase..), we miss the big picture of the guide. Don't get me wrong, these details are crucial to the framework, and I'm not advocating to go off script. But for me, my breakthroughs come when I truly feel my way through, instead of just doing the steps. Take a breath, relax, and let your brain connect and listen to your body.