only in so far as Dasein has been disclosed has it also been closed off; and only in so far as entities within-the-world have been uncovered along with Dasein, have such entities… been covered up (hidden) or disguised. Disclosedness is essentially factical.
This passage establishes the constitutive co-implication of disclosedness and closedness, grounds disclosedness in thrownness, and asserts its irreducibly factical character as a structural feature of Dasein’s Being.
, Being and Time, 1962thesis