The marquis, on the other hand, is pretty sure he exists, but isn't always so sure about the external world.
What about you lot out there? Do you believe you're real? If so, why and how? Conversely, do you believe that the external world is real, and if so, why and how?
(I believe in the external world because that's clearly where all the power and control and entitlement comes from, and where all the important things are.)