The three-word formula originated in his 1945[6] lecture "Existentialism Is a Humanism", though antecedent notions can be found in Heidegger's Being and Time.
To Sartre, "existence precedes essence" means that a personality is not built from a previously designed model or for a precise purpose, because it is the human being who chooses to engage in such enterprise.
While not denying the constraining conditions of human existence, he answers to Spinoza who affirmed that people are determined by what surrounds them.
As Sartre puts it in his Existentialism is a Humanism: "man first of all exists, encounters himself, surges up in the world – and defines himself afterwards".
Sartre is committed to a radical conception of freedom: nothing fixes our purpose but we ourselves, our projects have no weight or inertia except for our endorsement of them.
[13][14] Simone de Beauvoir, on the other hand, holds that there are various factors, grouped together under the term sedimentation, that offer resistance to attempts to change our direction in life.
A central theme is that since the world "in-itself" is absurd, that is, not "fair", then a meaningful life can at any point suddenly lose all its meaning.
The reasons why this happens are many, ranging from a tragedy that "tears a person's world apart", to the results of an honest inquiry into one's own existence.
Albert Camus, for instance, famously claimed in Le Mythe de Sisyphe that "There is only one truly serious philosophical problem, and that is suicide".