I became aware of just how fleeting the sense of happiness was, and how flimsy its basis: a warm restaurant after having come in from the rain, the smell of food and wine, interesting conversation, daylight falling weakly on the polished cherrywood of the tables. It took so little to move the mood from one level to another, as one might push pieces on a chessboard. Even to be aware of this, in the midst of a happy moment, was to push one of those pieces, and to become slightly less happy.