The Skeptical Premise
A skeptical hypothesis is the possibility of a state of affairs in which our knowledge of the world is erroneous and deceptive. For example, the famous 'brain in a vat' scenario.
Epistemological skepticism argues that we cannot have knowledge until we can rule out the skeptical hypotheses: The skeptical hypotheses cannot be ruled out, hence we do not have knowledge.
This argument however rests on a premise about the nature of knowledge, and the truth of this skeptical premise is simply being assumed without proof or demonstration.
Apart from a skeptical bias, there is no reason to assume that knowledge is impossible until the skeptical hypothesis has been ruled out.
Epistemological skepticism cannot be refuted, but the simplest way to avoid its conclusion is to not accept the skeptical premise in the first place.