A Crab said to her son: "Why do you walk so one-sided, my child? It is far more becoming to go straight forward." The young Crab replied: "Quite true, dear mother; and if you will show me the straight way, I will promise to walk in it." 

The mother tried in vain, and submitted without remonstrance to the reproof of her child. 

Moral : Example is more powerful than precept.