Karma

"You are born poor in this life on account of your past evil karma. He is born rich on account of his good Karma. So, be satisfied with your humble lot; but do good to be rich in your next life. You are being oppressed now because of your past evil Karma. There is your destiny. Be humble and bear your sufferings patiently. Do good now. You can be certain of a better and happier life after death."

The Samyutta Nikaya states:

"According to the seed that’s sown,
So is the fruit you reap there from,
Doer of good will gather good,
Doer of evil, evil reaps,
Down is the seed and thou shalt taste
The fruit thereof."