One who possesses virtue in its fullness resembles a newborn child.
Poisonous insects will not sting him, fierce animals will not attack him, predatory birds will not seize him.
His bones are weak, his muscles are soft, yet his grasp is strong. He has not yet experienced the union of man and woman, yet his genitalia will be erect. Indeed, his life force is at its peak! All day he cries but does not become hoarse. Indeed, his inner harmony is at its height!
To have inner harmony is to be in accord with the eternal, and to be in accord with the eternal is to be enlightened.
To force the growth of your vitality is ill fated. To direct the life force with the mind will make your strong, but creatures that are strong in this way soon are exhausted. This is not in accord with the Tao, and that which is not in accord with the Tao soon comes to an end.
(from Tao Te Ching, verse 55, translation by Robert Brookes)