"For all I know, my brain is making this all up," If you're going that far, why not take another step: for all you know, the entire context that convinced you

"For all I know, my brain is making this all up," If you're going that far, why not take another step: for all you know, the entire context that convinced you that you have a 'brain' is something your mind made up, too. Ultimately, there is nothing that you can't be wrong about.