The world-historical context in which Heidegger raises the question of Being is one which he has described as “the darkening of the world, the flight of the gods, the devastation of the earth, the transformation of men into a mass, the hatred and suspicion of everything creative" - J. L. Mehta
Sartre and Freud were not the only thinkers to lament our penchant for self-deception. The expert on the subject, in all its nuances, was German philosopher Martin Heidegger.
Known best for his first book Being and Time, Heidegger's initial concern in the book is the identity of the questioner of life - the questioner of Being. Who is the person who thinks philosophically? What does he know about his subject of interest, and what does he know about himself? Is it possible for him to come upon his quarry - the nature of Being and meaning of existence - before he first possesses Self-knowledge? Not according to sages of the first rank.
Heidegger insists that the latter inquiry is of greater philosophical importance, since Being is rather an elusive and, arguably, impenetrable mystery. In Being and Time, the author successfully refocuses attention on the questioner of life and seeker after meaning.
…to work out the question of Being adequately, we must make an entity, the inquirer, transparent in his own Being - T. B. Yagi
Being itself could not be experienced without a more original experience of the essence of man and vice versa - Martin Heidegger
It was a direction first explored by German philosopher Immanuel Kant. Technically, in philosophy, it is the province of Epistemology, the branch of philosophy concerned with what there is to know, and how we come to know about it.
Prior to Kant’s time the focus was on the branch of philosophy known as Metaphysics. By and large, metaphysicians concentrate on abstract problems, such as the existence and nature of God and substance of reality, etc. However, metaphysicians rarely delved deeply into the nature of consciousness itself. Metaphysics is closer to theology or religion, in that the identity of God takes precedence over the identity of man. The very term metaphysics means "beyond" or "greater" than the physical.
Metaphysics, and the questions it gave rise to, dominated the attention of thinkers from the era of Plato and Aristotle onwards. The Neo-Platonists, Plotinus and Porphyry, etc, were metaphysicians, as were all the Christian "scholastics" who followed them. Aquinas, Anselm, Augustine, Dun Scotus, and so on, can be listed as metaphysicians.

…Heidegger takes his central task to be the overcoming of metaphysics - Julian Young
Heidegger didn’t think much of the metaphysical tradition. He knew it inside-out but thought that philosophy had been seriously derailed by the those lost in metaphysical abstraction. The bulk of his writings brilliantly deconstruct the precepts and principles of metaphysics. He doesn't leave much standing.
Heidegger had more in common with ancient pre-Socratic sages, namely Heraclitus and Parmenides. Commenters see signs of eastern traditions in Heidegger’s writings, and debate about whether he was influenced by Taoism, Zen and other oriental schools of thought. Heidegger’s later writings tend to be mystical in complexion. His thought certainly influenced the founders of the deep-ecology movement. Poetic allusions to nature are to be found throughout his books and lectures, and he ended his academic career pointing not to philosophy, per se, but to poetry, art and craft as important and legitimate paths to truth.
Indeed, Heidegger’s writings not only concern the being who asks questions about Being, but also the whole problem of Truth and what it is.
This unique entity which raises the question of Being is not a chair, a fork, or a tree; it is rather the sort of entity that can make Being as its concern and Heidegger calls this entity ‘Dasein’ - T. B. Yagi
…Dasein is an entity that understands its own being. Dasein exists; and this means it makes choices. It is distinguished from all other entities by comporting itself toward its own existence - Richard Sembera
Is truth merely a matter of subjective judgment, or is it something objectively certain? Indeed, what is a “subject?” Who is the person you take yourself to be?
If it turns out that a subject is little more than a pastiche of social customs and conventions, is it likely such an artificial construct can apprehend truth? Surely, a man must first be a wholesome Self before that can happen.
