Thanks for clarifying. I would say that we need to be careful to distinguish being able to use quantum mechanics, and feeling that we really understand the implications.
In fact, the same applies even in more classical circumstances. For example, we know how to calculate the motion of a projectile under the influence of gravity. We could start worrying about unanswered questions such as why gravity exists, why it is always attractive (as opposed to electromagnetic phenomena), and on so on (see the Simile of the Arrow :)), but those questions do not need to be answered if all we want to do is calculate how high the ball we threw will go.