To be content with life or to live merrily, rather all that is required is that we bestow on all things only a fleeting, superficial glance; the more thoughtful we become the more earnest we grow.
Just as we outgrow a pair of trousers, we outgrow acquaintances, libraries, principles, etc., at times before they're worn out and times - and this is the worst of all - before we have new ones.