"He turned away; he didn't feel he could bear it. He was terribly afraid that happiness might be a habit, or a quality knitted into the temperament; or it might be something you learn when you're a child, a kind of language, harder than Latin or Greek, that you should have a good grasp on by the time you're seven. What if you haven't got that grasp? What if you're in some way happiness-stupid, happiness-blind? It occurred to him that there are some people, ashamed of being illiterate, who always pretend to others that they can read. Sooner or later they get found out, of course. But it is always possible that while you are valliantly pretending, the principles of reading strike you for the first time, and you are saved. By analogy, it is possible that while you, the unhappy person, are trying out some basic expressions - the kind of thing you get in phrasebooks for travellers - the grammar and syntax of this neglected language are revealing themselves, somewhere at the back of your mind. That's all very well, he thought, but the process could take years. He understood Lucile's problem: how do you know you will live long enough to be fluent?"
From A Place of Greater Safety by Hilary Mantel.