Your life does not get better by chance. Your life gets better by change. And there's something enlightening about knowing that, this is the one true universalist change. Heraclitus famously stated that, "no man ever steps in the same river twice."

In the same way that you can never have the same day twice.

So the existentialist question that Sartre has already posed is whether you let change happen to you or whether you become the agent of your own change.

Sartre stated that this cannot be done in a neutral manner. After all, everyone else around you is changing as well. As a result, Sartre believes that the definition of existentialism isn't simply what you choose to do, but what you choose to do with what others have done to you, which means accepting your fate and realising that you can change your fate. And that growth is dependent on change rather than chance.

That is Sartre's existential idea.