The effortless ease with which humans move our arms, our eyes, even our lips when we speak masks the true complexity of the control processes involved. This is evident when we try to build machines to perform human control tasks. While computers can now beat grandmasters at chess, no computer can yet control a robot to manipulate a chess piece with the dexterity of a six-year-old child. (which is why I play chess against 6 year olds).
Professor Daniel Wolpert explains how the brain deals with this and demonstrated that a key feature of skilled human motor performance is the ability of the brain to perform optimally in the presence of uncertainty.