French existentialist (1905-1980). Argued that human beings have no fixed nature: we are condemned to be free, and we define ourselves through our choices. Inauthentic flight from this freedom is “bad faith”.
Man is condemned to be free; because once thrown into the world, he is responsible for everything he does.
Everything is absurd. Imagine dinner with your partner. A Sartrian would see this as such: When your planet has turned away from a distant hyrdogen explosion, you put your knees under a slab of carbon and put dead mammals and plants in your mouth while another mammal is doing the same beside you.
The absurdity is in itself liberating, we have true freedom. Everything is possible, we can cast away any shackles.
We are in bad faith when we force ourselves to do something that we do not want to do, things that we do when we fall to external pressures of society to adopt false values and disown our innate freedom as sentient human beings.