"Man is fully responsible for his nature and his choices"

Jean-Paul Sartre asserts that human beings hold complete responsibility both for their essence and for the decisions they make throughout their lives. Sartre’s existentialism denies the existence of a predefined human nature set by any divine or external entity. Instead, it is the individual's freedom and conscious decision-making which shape who they are. Every action, choice, value, and project an individual undertakes defines them and, at the same time, demonstrates their capacity for self-determination. There is no appeal to fate, hereditary traits, or external excuses; each person must own both their being and their actions.

To say that man is responsible for his nature highlights the existentialist belief that "existence precedes essence". Humans are not born with an essential self; rather, they create their own essential characteristics through what they choose to do. One is not cowardly, heroic, generous, or selfish by destiny, nature, or circumstance, but by the way one acts and lives. This immense responsibility yields both possibility and anxiety. The burden of freedom can be heavy, without a blueprint for living, each individual must navigate the ambiguities and complexities of existence on their own, inventing values and priorities as they go.

Responsibility for choices further amplifies the scope of personal accountability. Every choice, large or small, is made in freedom and cannot be shifted onto others, society, upbringing, or even abstract concepts like "human nature". Avoiding choice is itself an act of choosing, what Sartre would call "bad faith", an act of self-deception where one pretends not to be free. For Sartre, authentic living means acknowledging the weight of personal freedom and accepting the consequences and implications of all actions and attitudes, thereby fashioning one's being in accordance with one’s own truths, unmediated by external scripts or excuses. Sartre challenges each individual to realize that the meaning of their life is not found but made, and to accept that burden is the foundation of genuine human dignity.