The bias runs deep. Few of us, surely, think of ourselves as having a fixed, monochrome personality: we’re happy or sad, stressed or relaxed, depending on circumstances. Yet we stubbornly resist the notion that others might be similarly circumstance-dependent. In a well-known 1960s study, people were shown two essays, one arguing in favour of Castro’s Cuba and one against. Even when it was explained that the authors had been ordered to adopt each position based on a coin-toss – that their situation, in other words, had forced their hand readers still considered that the pro Castro author must be deep down, pro Castro and vice versa.