Known unknowns, unknown unknowns, unknown knowns

Is ignorance a thing of laughing at or lamenting the inanity and mental indolence of most of us, or a thing of identifying educational failures which could be remedied?    

Daniel R DeNicola, in his book Understanding Ignorance: The Surprising Impact of What We Don't Know (MIT Press, 2017), puts ignorance under three categories:

Known unknowns: what we know we don’t know

Unknown unknowns: what we don’t know, we don’t know

Unknown knowns: what we don’t know we know    

Most of us mistakenly see ignorance as just the absence of knowledge. Given that philosophical literature lays more emphasis on having broad discussion on knowledge than ignorance, we think the latter doesn’t warrant weighty philosophical attention.    

It’s philosophically difficult to explain accurately what ignorance is. Even if it is just the absence of knowledge, ignorance has a right for philosophical attention of its own in an expanded array of philosophical debates.