We must see that this "I" and "mine" is the root cause of all forms of Dukkha. Wherever there is clinging, then there is the darkness of ignorance. There is no clarity because the mind is not empty; it is shaken up, frothing and foaming with the feeling of "I" and "mine". In direct contrast, the mind that is free of clinging to "I" and "mine" is serene, filled full of truth-discerning awareness.
So, we must firmly grasp the fact that there are two kinds of feeling: that of "I" and "mine", and that of truth-discerning awareness, and that they are totally antagonistic. If one enters the mind the other springs out. Only one can be present at a time. If the mind is brimful of "I" and "mine", truth-discerning awareness cannot enter; if there is truth-discerning awareness, the "I" and "mine" disappears. Freedom from "I" and "mine' is truth-discerning awareness.
From Buddhadasa Bhikkhu: Heart-wood from the Bo Tree 1