Why do you believe that some people are good and others bad
I believe that some are good and some are bad because I observe, through their actions, good and bad people. Hence they both exist. That's why I believe some are good and some are bad. And that was the question.
I asked why some people are good and others are not.
That's a new question. In my opinion, the combined effects of genetics and environment/upbringing unique to each individual cause a development of a set of morals or lack thereof.