Certain personality traits are linked to a tendency toward exceedingly selfish behaviors. There may be a huge gap between the selfishness of a narcissist and that of a psychopath, but current research shows that all negative personality traits share the same dark core.
Egoism, Machiavellianism, moral disengagement, narcissism, psychological entitlement, psychopathy, sadism, self-interest, and spitefulness are all negative personality traits recognized in psychology.
Some of them, such as sadism, rely on other people’s pain and discomfort for personal satisfaction.
Others, such as egoism, mean simply that a person is likely to place their own advantage first and foremost.