If you can't show that it's true, then you can't call it truth. Knowledge is similar to truth in that it a justified belief. Knowledge is demonstrable and testable with measurable accuracy. If you can't demonstrate your knowledge to any degree at all by any means whatsoever then you don't actually know what you think you do, no matter how convinced of it you are. Without evidentiary support, then it is only an empty assertion unworthy of serious consideration.

Patheos - The Cow (January 22, 2016)