‘You are a slow learner, Winston.’
‘How can I help it? How can I help but see what is in front of my eyes? Two and two are four.’
‘Sometimes, Winston. Sometimes they are five. Sometimes they are three. Sometimes they are all of them at once. You must try harder. It is not easy to become sane.’

George Orwell

1984. Part 3, Chapter 2. O’Brien interrogating Winston.