Humans have hundreds of skeletal muscles dedicated to locomotion and balance. Even those not directly related are sometimes needed to stabilize us. We need that because our body plan is fundamentally unstable. Falling over is the default state of human...

The few dozen actuators we can fit into a robot have a hard time managing that. We just don't have anything that adequately simulate muscles. Our motors and pistons can to incredible things, but they just don't behave like muscle...