You think, therefor you are. But am I? Do I exist because you think I think? But what if I think you don't exist? Does me not thinking you exist invalidate your existence, or is it further proof you exist? But how sure can you be that I exist? What's madness if just an altered perception of reality? Did you take the red pill, or the blue pill? Do either pills exist? I exist, but that's just me telling you I do, so how trustworthy can you be that I'm not just in your head? If I am in your head though, then believe it when I say that you exist, because you think, therefor you are.