Rabbi Meir said, " When a man teaches his son a trade, he should pray to the Possessor of the world, the Dispenser of wealth and poverty; for in every trade and pursuit of life both the rich and the poor are to be found. It is folly for one to say, 'This is a bad trade, it will not afford me a living;) because he will find many well to do in the same occupation. Neither should a successful man boast and say, 'This is a great trade, a glorious art, it has made me wealthy; ' because many working in the same line as himself have found but poverty. Let all remember that everything is through the infinite mercy and wisdom of God."
Rabbi Meir on Trades, Wealth, and the Dispenser
Kiddushin 82a (Harris, Hebraic Literature, 1901)