Cartesian rule cogito ergo sum is like a foundation of all Rene Descartes’s philosophy. It points to the essential relationship between subject’s own thinking and his being. How are we to understand that relationship? A thoughtful approach to that brings us to the conclusion that our being – mentioned in the Cartesian rule – must inevitably possesses a proper complex structure. This is so because our present thinking is possible at all for us only thanks to our participation in that specifically given being. Analyses carried out in this paper aim at showing how our thinking is necessarily conditioned by that complex way of being where the essence of our existence is being realized.