A sociopath is a person who has no conscience but has effectively learned how to manage his way through a life where few people can detect that they are different than him. Sociopaths are often charming and likable, but they can be frightening in their tactics, such as lying, to get what they want when they want it.
Lack of Conscience A sociopath more often than not has the rest of society fooled with his brash and coldhearted ability to have no remorse or guilt--no matter who the person he is affecting is--and to have no care about the well-being of others. A sociopath has no conscience and, therefore, has a make-believe step-by-step scenario life of doing whatever she wants and covering it up with a false sense of sincerity by masking that anything about her (and her psychological makeup) may be different than you.
Thrill Seeking A sociopath's job is to get as much thrill out of his victim as he can, but not get caught. They manipulate, cheat, lie and color situations for no purpose but to get some satisfaction out of the fact that they can bring another person down, and easily. To someone who has no conscience, it is easy to tell a little white lie about a co-worker, to manipulate a lover and make them feel inferior, or to make promises to get people on her side, only to find that those promises were false. This is all easy to do because the person has nothing within him telling him that it is morally wrong.
Opposing Extremes A sociopath may want to rise to power and use her lack of a conscience to manipulate large groups of people, with or without blood lust. A terrorist is an example of someone who has no conscience and an affinity for harming others in a violent manner. There are also sociopaths who will want to just try to get by with as little effort as possible. They will use up the resources of everyone around them until the rivers run dry and then move on to their next victim.