"I think, therefore, I am." is the foundational precept of existentialism. Then, this becomes a struggle with what to do with our existence. Next, it divides into two viewpoints - one atheistic and the other theistic in their general understanding and approaches toward resolution.

If what you are saying is true, other than René Descartes' ethereal statement, Can he prove that he exists, or less obtusely, that evolution of the species is a real phenomenon, or some other theory... maybe time and/or relativity? I'm sure you're smart enough to think of some other appropriate challenge not related to metaphysics.

I believe in God, Jesus. and the Bible. I know they exist because each, in turn, has changed my existence from disaster to rescue and recovery - physically, mentally, inwardly, and in real living (like vocationally)...