Existence precedes essence — we are not born with a fixed nature

Sartre's foundational claim inverts the traditional view that humans are made according to some prior concept or purpose, the way a manufactured object like a paper knife is made according to a design that precedes its existence. For humans, Sartre argues, there is no such blueprint: without a creator God to conceive of us in advance, we simply exist first, and only through living, choosing, and acting do we gradually become whatever we turn out to be.

This means there is no human nature in the sense of a fixed set of traits or purposes that everyone shares before they act. What people call "human nature" is, for Sartre, really just the sum of choices humans have made and continue to make, not a template dictating those choices in advance.

This single reversal underlies nearly everything else in the lecture: if essence doesn't precede existence, then no external authority — religious, biological, or social — can hand a person their identity or purpose ready-made.

Takeaway: you don't discover who you are — you create it, action by action, with no predetermined script to follow.