The calipers are strong enough to grip the spinning rotor on a vehciel which
weighs over 4000 lbs. You cannot possibly exert that much pressure with your
bare hands. That is why the pistons seem very hard to push in.

OK, I am not including the Hulk and Superman in the above equation. But then
the Hulk's hands are too big to big the caliper area. Superman probably could.
=)

BenT