You reap what you sow. That being said, not all reap what they sow. And some reap what others sow. Yet others reap without any sewing done by anyone.
You are punished for your sins. Yet some are never punished for their sins. Yet some are punished having never transgressed that sin. And yet others are given light punishment for grave sins, and others are given heavy punishment for light sins.
Basically, there is no justice in this world. Don't count on good things happening because of your good deeds, or bad karma upon bad people. Don't count on society or laws to secure or redeem you or punish others.
You do things, good or bad, ultimately only because it feels good to you. If you are a good person, you feel good doing good things and feel bad doing bad things. Bad people feel good doing bad things and don't care about doing good things. If you think yourself a good person, you may also think that you are a moral person. But frankly, that's just a label.