It‘s just crazy to me that this guy lives around the corner. That should inspire some hope for me I guess, that even people from Vienna can be successful on such a level.
Let R = {X \notin X}, i.e. all sets that do not contain themselves. Now is R \in R? Well this is the case if and only if R \notin R. But this clearly cannot be.
Like the barber that shaves all men not shaving themselves.