In Text 11 Krishna said, mama vartmanuvartante manusya sarvasah - "For everything, people come to me." This means that whatever one receives from providence is given by Krishna. Some people receive terrible misery from providence. Is this Krishna's fault? Is he responsible for our happiness or suffering?
Krishna here explains that he created the system which rewards and punishes persons who perform good or evil - catur-varnyam maya srishtam guna-karma-vibhagashah. However, it is not he who performs the good or evil actions. He created the actions, he also created their rewards or punishments, but it is us, not he, who perform the actions and are thus deserving of their rewards or punishments.
It is like a person who invents a game. He creates the game board and the rules for winning or losing. However, the way you play the game is the cause of your victory or defeat. Krishna set up the material world with it's rewards and punishments, but he allots us the freewill and independence to freely choose how we "play the game". Thus we, not he, are responsible for the happiness or misery we encounter.
Catur-varnyam - The Four "Colors"
There are four varieties (or "colors") of human inclinations. There are (1) those inclined to labor with the hands, (2) those inclined to produce and trade goods and commodities, (3) those inclined to govern and protect others, and (4) those inclined to understand, teach and guide others.
In ancient India they were known as sudra, vaishya, kshatriya, and brahmana, respectively. In feudal Japan there was the artisan, the merchant/farmer, the samurai, and the priestly. In old Europe was the proletariat or surf, the bugeous, the kings, and the priest. These four types of human inclination are globally present, as they are created by God.
Krishna created the four social orders corresponding to these four human inclinations, with their respective characteristics (guna) and duties (karma). Performing these duties brings prosperity and neglecting them brings suffering. This system created by Krishna helps the conditioned soul favor behavior conducive to his purification, happiness, and gradual liberation.
Kartaram, Akartaram - The Actor who Never Acts
Krishna acted in creating the four social types and the concomitant system of punishment and reward. In that sense he is active (kartaram). However, he does not act within those roles, and in that sense is inactive (akartaram).
Are we the cause of our own happiness?
Yes. However, a saintly person may often be heard saying that God is kind to bestow happiness upon him. This does not contradict the above principle, for God takes special care of those who depend upon him. The principle above is for those who depend upon their own efforts entirely. A saintly person rightly feels that he deserves much suffering from his previous evil deeds, yet God has kindly pardoned him and grants happiness instead.