Which side of the fence?

I was speaking to my son the other day and having walked both sides of the fence he had asked me, What makes a person good or bad? Could a bad person do good things and could not a good person do bad things? From my experience yes a person could be good and do bad things and vice versa. It is when one form takes the majority that there is change in the person or so I believe. Someone can be bad for a very long time and yet do good things to people he or she cares about. That should not be mistaken for good, it is just kindness shown to a few key people. Practing the longevity of good acts without the acts of evil over time I believe makes a person good. Although one could always argue their motive......I have just made myself unsure as to wheather there is a difference. I will think on this more and get back to you.