Who said “Man is the only animal for whom his own existence is a problem which he has to solve.”?

“There is no means of proving it is preferable to be than not to be.”

“Existence itself does not feel horrible; it feels like an ecstasy, rather, which we have only to be still to experience.”

“One is still what one is going to cease to be and already what one is going to become. One lives one's death, one dies one's life.”

“The cradle rocks above an abyss, and common sense tells us that our existence is but a brief crack of light between two eternities of darkness.”

“I can, therefore I am.”

“Man's biological weakness is the condition of human culture.”

“Only the person who has faith in himself is able to be faithful to others.”

“The successful revolutionary is a statesman, the unsuccessful one a criminal.”

“Love is the only sane and satisfactory answer to the problem of human existence.”

“To die is poignantly bitter, but the idea of having to die without having lived is unbearable.”

“Immature love says: ''I love you because I need you.'' Mature love says: ''I need you because I love you.''”