Decartes also said that he must have been created by a more perfect being, i.e. God. This is another way of saying there must be another being. Whether that "more perfect being" is God or the universe, the first important thing is the sense of otherness.
As all experience begins in the womb, this sense of otherness also begins there. When we're born, the certainty of the womb is replaced by the uncertainty of the universe. The absolute truth of being, of never changing security, is wrenches from us. The otherness of the universe replacing the otherness of the womb.
We never recover, but we try anyway. We seek certainty, and absolute truth. Some of us find it in religion, while others find it in science and mathematics. Compared to the womblike experience, these alternatives are very abstract. They're less satisfying, but they're all we have.
We can never recover, but we try anyway.