How does Rene Descartes come to the conclution that Cogito Ergo Sum?

René Descartes arrives at the conclusion "Cogito, ergo sum" ("I think, therefore I am") through a process of radical doubt. He systematically doubts all beliefs that can be called into question, including the existence of the physical world and even his own body. However, he realizes that the very act of doubting or thinking is undeniable proof of his existence as a thinking being. Thus, the act of thought becomes the foundational certainty upon which he builds his philosophy.