Right thru the first 3 of John Barth's novels, the male protagonists all suffer from a similar malady, that of having no specific ambition whilst also lacking in any sort of stable identity.

They manage to reason their way to a somewhat comfortable acceptance of this state of being. I have half a mind to copy down their reasoning(s) and repeat them to myself obsessively and basically try to "theft" a mindset from a novel, but we'll see.