It is an interaction between circumstances and innate traits.
Materialists ascribe the innate traits to maternal heredity.
Reincarnationists to acquired traits of character, derived from past experience. Good and bad derive from the combination of the internal and external, and have no meaning in respect to either alone. It can be seen that the internal is really the governing factor, for a man with a certain view of life can be patient, placid, happy and healthy under disappointments and deprivations which make another miserable and poison him with the secretions set in motion through his body by envy, rancor, and greed. The internal condition is the result of habits of thought and feeling developed in past incarnations and in this present life. Environment is the rebound against the individual of the influences he exerted on man and nature at large in the indulgence of those habits in the past.