Yawn. Knowledge is impossible. You could be a brain in a vat or whatever.
Meanwhile, the rest of us have lives to live, and we can't waste our time rehashing the question of whether everything in our perception is a falsehood.
How do you know that Obama is really the President? Maybe Hillary Clinton really won in 2008, and has been President this whole time, but all media outlets and everyone who really knows is just lying to you. You're being manipulated!