Complex sentence: He argued that Western thinking had lost sight of being, and that by people finding themselves as "always already" moving within ontological presuppositions, they lose touch with their grasp of being and its truth thus becomes "muddled".
Split into simpler sentences: He argued that Western thinking had lost sight of being. Finding ourselves as "always already" moving within ontological presuppositions, we lose touch with our grasp of being and its truth becomes "muddled".