When is a translation "faithful" to the original?

The unnamed narrator/protagonist of Katie Kitamura's 2017 novel A Separation is a translator. Her profession is irrelevant to the main story, but at one point she muses about translating Balzac's story Colonel Chabert, "although not with particular success."

Katie Kitamura

She writes, "I had not been able to find the correct register for capturing the particular density of Balzac's prose, I generally translate contemporary fiction, which is an entirely different affair—the colonel of the title is presumed dead in the Napoleonic Wars."

Because Balzac was born in 1799 and his first book published in 1823 even he may have had difficulty finding the appropriate French register for his story written years after Napoleon. 

In any case, Kitamura observes that "translators are always worried about being faithful to the original, an impossible task because there are multiple and often contradictory ways of being faithful, there is a literal fidelity and there is in the spirit of, a phrase without concrete meaning."

Being faithful to the original is something I worry about when I translate Japanese. Because I'm translating popular, contemporary fiction—not "literature"—I believe most of the meaning is on the surface and I can do okay. But because I have to work so hard to understand many sentences, I'm sure I have not done some justice. 

The English I produce is interesting, reads well, and makes sense. Is it faithful to the original? I can only do my best and hope.