A little excerpt that helps me to convince myself that I actually exist:
But I have convinced myself that there is absolutely nothing in the world, no sky, no earth, no minds, no bodies. Does it now follow that I too do not exist? No. If I convinced myself of something [or thought anything at all] then I certainly existed. But there is a deceiver of supreme power and cunning who is deliberately and constantly deceiving me. In that case I too undoubtedly exist, if he is deceiving me; and let him deceive me as much as he can, he will never bring it about that I am nothing so long as I think that I am something. So, after considering everything very thoroughly, I must finally conclude that the proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind.
In essence, I THINK THEREFORE I AM.
This is Renee Descartes, but many others have proposed the same idea. It doesn't quite give me the answer, but it at least provides somewhat of a logical response to the most fundamental of all questions: do I even exist? The answer is: yes, if I am thinking, have thought, or have the capacity to think, then I must exist, for how could something that doesn't exist have thoughts?