While Heidegger contends that this is not only human action, the constant revelation occurs when man permits himself to be a character in the setting upon challenges to nature. Man can set upon what was already concealed as he responds to the call of unconcealment, but "when man, investigating, observing, pursue nature as an area of his own conceiving, he has already been claimed by way of revealing that challenges him to approach nature as an object of research, until even the object disappears into the objectlessness of standing-reserve".