Tao Te Ching 55

He who has in himself abundantly the attributes of the Tao is like an infant. Poisonous insects will not sting him; fierce beasts will not seize him; birds of prey will not strike him.

The infant's bones are weak and its sinews soft, but yet its grasp is firm. It knows not yet the union of male and female, and yet its virile member may be excited, showing the perfection of its physical essence. All day long it will cry without its throat becoming hoarse, showing the harmony in its constitution.

To him by whom this harmony is known,
The secret of the unchanging Tao is shown,
And in the knowledge wisdom finds its throne.
All life-increasing arts to evil turn;
Where the mind makes the vital breath to burn,
False is the strength, and o'er it we should mourn.

When things have become strong, they then become old, which may be said to be contrary to the Tao. Whatever is contrary to the Tao soon ends.