Jade and men, both are sharpened by bitter tools

Similar sayings:

Customers are jade; merchandise is grass Customers are jade; merchandise is grass
A bad worker quarrels with his tools A bad worker quarrels with his tools
A bad workman blames his tools A bad workman blames his tools
Defeat isn’t bitter if you don’t swallow it Defeat isn’t bitter if you don’t swallow it
A jade stone is useless before it is processed; a man is good-for-nothing until he is educated A jade stone is useless before it is processed; a man is good-for-nothing until he is educated

Chinese sayings and proverbs