Knowledge does not necessarily equate to truthfulness.

"Knowledge as justified true belief (JTB)
The JTB account of knowledge is the claim that knowledge can be conceptually analyzed as justified true belief, which is to say that the meaning of sentences such as "Smith knows that it rained today" can be given with the following set of conditions, which are necessary and sufficient for knowledge to obtain:

A subject S knows that a proposition P is true if and only if:
      P is true, and
      S believes that P is true, and
      S is justified in believing that P is true
The JTB account was first credited to Plato"- wikipedia

To get over Gettier's problem one can just remove the first clause (P is true). We all might be just brains in a jar in some other dimension we cannot comprehend. However, we can with confidence say that we have knowledge that the Earth is round.

Knowledge is a justified falsifiable belief. Which is not the same as a justified true belief.