I believe I exist.
I see a beer to my left, of which I just had a sip.
I see these fingers in front of me typing what I believe are words which I believe will be read and understood by some other I's.
I just had a notion that I am hungry, but a thought raced across with the message that I need to lose some weight because I just had a hip transplant. I believe so anyway.
I believe I just coughed.
I believe I exist. Yes.
And YOU can't prove my belief wrong either. So there.