There is nothing softer and weaker than water.
And yet there is nothing better for attacking hard and strong things.
For this reason there is no substitute for it.
All the world knows that the weak overcomes the strong and the soft overcomes the hard.
But none can practice it.

Lao-tzu (604?-531? BC) Chinese philosopher, poet [also Lao-tse, Laozi]

Tao-te Ching, ch. 78 [tr. Wing-Tsit Chan]