I really enjoy the philosophy of the 80/20 rule for running (Book from Matt Fitzgerald), which says that 80% of your training should be at level 2, where your heart rate is much lower. It's made it a lot easier to actually go run every day, as it doesn't leave me feeling exhausted and it changes the psychology from feeling like I need to run faster to actually needing to slow myself down, which is really transformative for me in particular. YMMV, pun intended.