A man in the undifferentiated mode never questions the meaning of his own life or faces up to the fact that his existence is defined by the culture fate threw him into. He never recognizes his own thrown-ness, but blindly accepts the existence he has inherited.
A man in the inauthentic mode recognizes that his existence is a result of coincidence -recognizes his own thrown-ness, but simply substitutes some other role for the life he inherited. It is like a man who is born into a family of farmers and decides he's going to be a doctor rather than a farmer. He has substituted one rule for another without recognizing that both roles were created by the culture or world he was thrown into.
A man's recognition of his own thrown-ness sometimes leads to what Heidegger called anxiety. Anxiety is the result of man's realization that anything he might possibly do has already been defined in advance by the culture he was thrown into. He begins to think about death. When is unable to face up to the possibility of his own non being or nothingness, Heidegger referred to this as fallen-ness. Instead of dealing with his anxiety the man who experiences fall in this returns to the inauthentic mode.
But some that experience anxiety are able to face up to their own thrown-ness and their own death. While all ways of life are defined by the culture we inherited, each of us has to die on our own. Given that we are responsible for our own death, we become responsible for our own life. Heidegger called this care. In caring for the world, each man makes the most of his own possibilities - even if those possibilities were originally dictated by the culture he was thrown into. A man who adopts this attitude lives in what Heidegger called an authentic mode of existence.
So wrote clew in