This is a bit complex issue. I am still trying to figure out how to get all the relevant factors into a single post.
By the way, Johnny_Lim and Akvan have pointed out the important of the five niyamas. However, the traditional interpretation of the five niyamas is not correct.
I have discussed this a bit at: “What is Kamma? – Is Everything Determined by Kamma?”
I hope to finish the post within a few days.