I agree with that quote. However, no one here is saying they never wonder or that they are dead sure about everything.
What we are saying is that when all evidence points to one conclusion, throwing your hands in the air and saying, "Well, we can never know anything!" is just fucking stupid.
Yes, it is true that we fallible mortal monkeys are limited by our senses and experiences and everything could be an illusion, but it is completely pointless to live according to that. We have to learn from observation and experience. It's all we have.