The moment an artist starts watching themselves create - worrying how it looks, what others will think - the work stiffens. Bradbury argued that the best writing comes from working fast and with passion, letting the subconscious lead before the inner critic arrives. The idea echoes the Zen arts of archery and calligraphy, where mastery means acting without the interference of the self-regarding ego, and modern research on "flow", in which self-awareness fades as absorption deepens. Bradbury's full sentence goes further, to "living itself": we are rarely more awkward than when performing ourselves, and rarely more alive than when we forget to.
Stop watching yourself. Start making.