Bellow is describing something more troubling than simple stupidity—he's naming the active work we do to stay blind, the clever arguments we manufacture when reality threatens something we desperately need to believe. Notice he says "intelligence," not its absence; we're not talking about dim people but sharp ones who've turned their faculties toward self-deception. A person might marshal impressive evidence to convince themselves their partner hasn't changed, or their career choice wasn't a mistake, not because they lack the capacity to see, but because the alternative is unbearable. The quote's real sting is that it makes ignorance look less like an accident and more like an exhausting accomplishment.