Following partially Berkeley’s conclusion, Hume also concluded that we have no access to the thing-in-itself. It is always indirect knowledge. It is always the representation. Schopenhauer concluded that we have access to one special thing – the self. It being so, this being the will, as opposed to representation. But I will contend that the will is also secondhand access.
Like the things “outside” we can know it only through sense perception. The self “inside” is also known only through sense and perception. The feelings and emotions are only ever representations themselves.
Two things, then. There is no direct access to anything, including to the self. And secondly, there is strictly nothing to be inside or outside.