A central proposition of existentialism is that existence precedes essence, which means that the most important consideration for the individual is the fact that he or she is an individual—an independently acting and responsible conscious being ("existence")—rather than what labels, roles, stereotypes, definitions, or other preconceived categories the individual fits ("essence"). The actual life of the individual is what constitutes what could be called his or her "true essence" instead of there being an arbitrarily attributed essence used by others to define him or her. Thus, human beings, through their own consciousness, create their own values and determine a meaning to their life.[ Although it was Sartre who explicitly coined the phrase, similar notions can be found in the thought of existentialist philosophers such as Kierkegaard and Heidegger.
It is often claimed in this context that a person defines himself or herself, which is often perceived as stating that they can wish to be something—anything, a bird, for instance—and then be it. According to most existentialist philosophers, however, this would constitute an inauthentic existence. Instead, the phrase should be taken to say that the person is (1) defined only insofar as he or she acts and (2) that he or she is responsible for his or her actions. For example, someone who acts cruelly towards other people is, by that act, defined as a cruel person. Furthermore, by this action of cruelty, such persons are themselves responsible for their new identity (a cruel person). This is as opposed to their genes, or 'human nature', bearing the blame. As Sartre writes in his work Existentialism is a Humanism: "...man first of all exists, encounters himself, surges up in the world – and defines himself afterwards." Of course, the more positive, therapeutic aspect of this is also implied: A person can choose to act in a different way, and to be a good person instead of a cruel person. Here it is also clear that since humans can choose to be either cruel or good, they are, in fact, neither of these things essentially