Towards the end of Jane Austen’s Emma (1816), the heroine Emma Woodhouse has a moment of blinding clarity. Throughout the novel she has been treating her old friend and neighbour, Mr Knightley, as little more than a familiar sparring partner. But as she learns that her friend Harriet is harbouring dreams of marriage with him, the scales fall from her eyes. ‘It darted through her, with the speed of an arrow, that Mr Knightley must marry no one but herself!’