The skeptic's position is not that nothing can be known, it is that nothing can be known completely. Human senses are limited. We can perceive only a fraction. We rely on technology to improve upon our perception, although what our machines do is to gather input and convert it to a format our senses can use. There is always room for doubt because there may be unknown factors that we are as yet unable to perceive. To avoid the fallacy of appeal to ignorance, we rely on scientific methods to form, test, and revise hypotheses and theories about perceived phenomena.