We exist because, our existence is already there. There is no source of how long we have existed. We have existed for an indefinite amount of time, the possibility of finding out how ancient the reason for our existence is also does not exist.
Existence is indefinite.
Our existence is indescribable and inexpressible. The reason for our existence is very ancient, so ancient that its source is beyond infinity.
Existence of self.
We exist, universe exist , we all exist because of existence, infinite source of our existence. Therefore existence is reality.