I think, therefor I am.
But how do I know you think? You damn computer program!
Do you think? Or, are you lost in the limbo that I have entertained myself with that, OMG, these people are really nothing more, as far as I know for all my better knowledge, than a few characters and an avatar appearing on my screen.
But, I can prove my existence. If I gave my real name you would find it published in the news paper under those who are on the deans list for the past four or five years. I was also in the newspaper because I was standing outside a movie theater when Episode 1 tickets went on pre-sale (if you don't know what Episode 1 is, then you must prove your own existence to me).
And due to the computer programs I wrote in high school, without me, well, then, who is to say how different of a world this world would be? I did write a program for a hospital for their billing purposes, so, as far as I know, as far as I can let my imagination run wild, my existence may have prevented a hospital from going berserk which may have prevented gods knows what. I also made it easier for teachers at my high school to track semester grades when the school switched from 6-week grading periods to 9-week periods (please don't take me seriously on this), so I may have prevented an entire high school from going bonkers!
So, prove yourself, you, for all I know, a furry feline who somehow acquired the ability to type.