Yeah, also known as the "last Thursday" hypothesis (as in, everything was just poofed into existence last Thursday with all our memories and history intact). Pretty much useless as a way of describing the world. I wouldn't say that we take it on faith that we're not just Boltzmann Brains or some such, but insofar as we trust the evidence of our senses we trust that the outside world is real and can affect us directly and profoundly. It therefore follows that we can try to understand it on its own terms.
If we _can't_ trust our senses (and as human beings sometimes we actually cannot, take any optical illusion or hallucination for an example) then all bets are off. But as I said, that's just not a very useful way to view ourselves and the world.