Your body has operating modes.
Most runners apparently received the machine without reading the manual.
Easy is a setting. It isn't an accident. It isn't punishment. It isn't what happens when your legs are too wrecked to perform another workout.
Low-intensity running builds the machinery that lets you tolerate more work: aerobic enzymes, mitochondrial development, capillary density, cardiac efficiency, and the ability to keep producing energy without setting the metabolic kitchen on fire.
Then there's moderate running. Moderate isn't evil. ASCEND is not dispatching tactical units when your heart rate enters Zone 3.
The problem is accidentally living there. Too many runners turn every supposedly easy run into something vaguely purposeful — not hard enough to be a real quality session, but hard enough to add recovery cost. Then they wonder why the actual workouts suffer.
Remarkable mystery.
High intensity has a job too. Threshold. Intervals. Race-specific work. Use the correct setting for the correct purpose. That's training. Running whatever pace makes your ego comfortable that morning is cardio roulette.
Twenty-two beats of average heart rate. That's the gap between what runners call easy and what easy actually costs.