Karma

Karma.. Well, its something almost every Hindu believes in.. What is it? Logic is simple, its pretty much the same as Newton's 3rd law of motion.. For every action there is an equal and opposite reaction.. This action may either be good or bad.. But my question here is what is good and what is bad? Who decides it?

Take for example, A poor unemployed man who lives with his wife and 3 kids in a City suburb. His kids are under serious risk of malnutrition because of absence of food. This prompts the man to steal some fruits from a nearby Grocery store.
Assume you to be present in the same Grocery store. You have no idea about this person's history and you see him stealing those fruits right in front of your eyes. We all know stealing is a bad deed and you inform the shopkeeper about this incident and the poor unemployed man gets caught and jailed for a few months.

A day or 2 later after the stealing incident the kids die due to malnutrition. You assume that you did a good deed by letting the shopkeeper know about this guy stealing stuff from the grocery shop. But what eventually had happened is the "good"act that you performed resulted in the death of those kids.

So what is good and what is bad? Can somebody explain?