Understanding what we accept without question and ending our existence allows us to start seeing the world more critically, relying less on the senses and more on our mind. Starting over allows Descartes to see existence and reality from a fundamental perspective, without relying on previous aspects of knowledge. This allowed Descartes to conclude that existence is proven, but I believe it also helped Descartes differentiate reality and existence. Personally I believe that reality is our choice, existence is the result of it. We can choose to bring something into reality, but we cannot choose whether to do it