Check this post on Miami Bourbaki. Forgive the philosophy jargon, which in this case is sort of necessary, I'd like to share my argument with you. Heidegger is an important 20th-century philosopher who constructed a philosophy known as Existentialism, whose protagonist is Dasein (a German word for "man," "human"). Heidegger was interested in Dasein, but also in (b)eings: things. Harman takes Heidegger's philosophy, deconstruct it to make it work for the thing. In doing so, Harman destroys many of Heidegger's Dasein's appurtenances in order to build his own metaphysics which he calls tool-being (check my 3-point manifesto regulating metaphysics at the beginning of the post).