One of the main principles of existentialism is that human beings are free, self-conscious beings. This means that each human being must define who he is by accepting the responsibility that comes with freedom. Each human being is responsible for his actions and decisions; regardless of outside influence, he is fundamentally alone in an uncertain world.
Because human beings are free agents, and there is no single way to navigate life, it is impossible to safely predict the behavior of other agents. Sartre refers to this inescapable uncertainty as despair.
Nietzsche recognized that there is no meaning intrinsic to life; however, he believes that people can create meaning and value, depending on how they live their lives. Sartre continued this line of reasoning to arrive at another of the principles of existentialism : since there is no objective account of what it means to be human, each human being decides his own meaning through existence. Human beings are not fixed entities; instead, they decide what they become.
Alienation is also central to existentialism. Alienation refers to the fact that, while human beings can give the world meaning through their actions, the world is not brought into existence through human actions. Every human being is aware of the otherness of the world at various times; for example, self-awareness, he feels when he realizes that someone is looking at him. Every human being can choose his own actions, but he is also just part of the world for other people.
Another principle of existentialism is that of authenticity , which is concerned with self-formation. An existentialist considers an authentic life when a person chooses his actions based on his values and commits himself to them. An inauthentic person performs his actions because that is what is expected of him, and he acts passively.