Heelstriking being likened to “tapping the brakes.”
Situation 1: Get in your car. Go to a road with no traffic. Accelerate for one mile without touching the brake. Notice it’s smooth and seamless. This is equivalent to running with good form.
Situation 2: Now do the same thing, except this time tap your brakes about 140 times each minute as you drive the same mile. This is what you are doing when you overstride with a heel strike.