"I do not pretend to know where many ignorant men are sure." (Attributed, in various forms, to Clarence Darrow)
Our perception of external reality is sensory experience. Not just sensory input, but experience, a combination of sensory input and how a particular brain processes it.
"In philosophical skepticism, pyrrhonism is a position that refrains from making truth claims. A philosophical skeptic does not claim that truth is impossible (which would be a truth claim)."
Saying "I believe such and such" is to enforce ignorance on oneself. Belief and faith provide comfort against the unknown, the unpredictable, the uncontrollable, but, in reality, human understanding is so limited, that all "knowledge" is up for grabs. But "believing" is pervasive. What is its survival value, its reproductive benefit?
All answers are hypotheses. They have to be. We know that, at a fundamental level, we don't really know anything. We can't answer the most basic questions.
- What is the mind?
- What is consciousness?
- Why is the universe expanding? We literally invent stuff that we can't detect, "dark energy", to explain what we observe.
- What is gravity?
- What is matter? At the quantum level there is weird behavior we can't begin to explain. Particles separated in space that can affect one another. Particles that jump in and out of existence at random.
"The only true wisdom is in knowing you know nothing." Socrates
Philosophers can argue ad nauseum. In the end, our perception of external reality is sensory experience. Not just sensory input, but experience, a combination of sensory input and how a particular brain processes it. If that experience is an illusion, so what? It's all we have. To argue otherwise is just an intellectual exercise of no practical value. ( He said, arrogantly dismissing thousands of years of Philosophy. ;-) That isn't to say, however, that the "five senses" are, necessarily, the only sources of input.
It seems to me that belief is arrogant. In saying, "I know what is true.", one is saying, "I have so much knowledge and wisdom that no one can possibly challenge me." If instead one says, "I don't know", it implies, "I can still learn. I'm not all-wise, all-knowing." It's a humble statement, as well as a courageous one. See Living with uncertainty.