Those are heart rate zones, high intensity interval training (HIIT) is zone 5. Here's the first description I found: https://www.polar.com/blog/running-heart-rate-zones-basics/
Since it's interval training, just doing 10mins hard is not what's prescribed. It's more like doing repetitions of, say, 2 mins easy and 30s sprints.
I would recommend reading about stoicism and mindfulness. For me they felt like those things that are obvious but are super helpful to see explicitly stated. And have helped me learn to enjoy life more and set priorities for where/with whom I spend my most precious resource, my time.