This is not just lack of empathy, though that is one of the defining qualities. Psychopathy is a whole condition, in which many qualities are part of the total. It is more like being a human predator, who firmly believes (and acts on the belief) that the smart and proper way to live is to exploit, and prey upon fellow humans. It is very easy for an honest person to determine if he/she is a psychopath. Here is a test.
When I did this, I got only 3 points out of a possible 40. Those who get 30 are definite psychopaths. If you get 20, you are not, but you will be a person I would avoid. See how many points you get, and the honest people report back.
I scored a 3, but I think 2 of those were probably within normal parameters, ie others would score me a 1.\
I think the psycopath would score themselves quite low, as low as they think they could get away with, because it would be in their interest to do so. This needs to be an outside evaluation.