The Rules of Engagement: Betsy's Blitheness

The word is used three times in The Rules of Engagement. It might pass without notice were it not for the following, from some years later. In The Rules of Engagement 'blithe' describes the innocent, romantic Betsy. Here, in Brookner's 2009 Telegraph interview the word takes on more equivocal associations:

In Strangers it is the tentative, introspective Sturgis who is confronted with the impulsive, carefree and monstrously self-obsessed Vicky Gardner, whose only interest in him is in what he can provide for her.  The person who thinks seriously about life, Brookner's books suggest, who proceeds cautiously and conscientiously, will be punished for their virtue, end up alone and dissatisfied, while the person who takes a wholly unreflecting and rather selfish view of life pays no price for it. 

'But haven't you noticed that?' 

She gives an amused smile. 'Think of Tony Blair. Unrealistic. Selfish. Happy as a clam!'  Didn't Plato say the unexamined life is not worth living?  She gives the faintest smile. 'Plato could be wrong too. I think the unexamined life is much better. Much more comfortable.' So you wish you had been…  'Blithe…' It rolls off her tongue, wrapped in longing. A lovely word, I say.  'It's an old-fashioned word. You don't hear it much.'  So you envy the blithe?  'Oh yes.'