Understanding by Design by Wiggins and McTire

A person understands something when they can flexibly and fluidly apply what they know in a variety of contexts. You need to be able to recognize the applicability of knowledge in this other domain that tends to require kind of abstracting the knowledge to a greater degree. And your ability to understand and apply things in these new domains will vary based on the situation. So for instance, you aren't being really taxed by what's going on in this new domain won't make it easier for you to apply the stuff that you know from the old domain.