The title of this novel is actually a terrible mistake.
Wait, let us explain. First of all, it's from a quote by Taoist philosopher Zhuangzi that shows up as the epigraph to the third chapter of the novel. Check it out:
Those whom heaven helps we call the sons of heaven. They do not learn this by learning. They do not work it by working. They do not reason it by using reason. To let understanding stop at what cannot be understood is a high attainment. Those who cannot do it will be destroyed on the lathe of heaven.
—Chuang Tse: XXIII (3.0)
So, the problem here is that it's a terrible translation: China didn't even have lathes when this was written. Not to mention that a lathe is a pretty weird thing to choose for destroying stuff. We mean, look at it.
Okay, putting aside the silliness of the translation, why did Ursula Le Guin choose this line and this passage to represent her novel? To answer that, it might be a good idea to look at the whole passage in a slightly better translation:
He whose mind is thus grandly fixed emits a Heavenly light. In him who emits this heavenly light men see the (True) man. When a man has cultivated himself (up to this point), thenceforth he remains constant in himself. When he is thus constant in himself, (what is merely) the human element will leave him', but Heaven will help him. Those whom their human element has left we call the people of Heaven. Those whom heaven helps we call the sons of heaven. They do not learn this by learning. They do not work it by working. They do not reason it by using reason. To let understanding stop at what cannot be understood is a high attainment. Those who cannot do it will be destroyed on the lathe of heaven.— Chuang Tzu: XIII (Legge Translation)
Or this one:
He whose inner being rests in the Great Serenity will send forth a Heavenly light. But though he sends forth a Heavenly light, men will see him as a man and things will see him as a thing. When a man has trained himself to this degree, then for the first time he achieves constancy. Because he possesses constancy, men will come to lodge with him and Heaven will be his helper. Those whom men come to lodge with may be called the people of Heaven; those whom Heaven aids may be called the sons of Heaven.
Learning means learning what cannot be learned; practicing means practicing what cannot be practiced; discriminating means discriminating what cannot be discriminated. Understanding that rests in what it cannot understand is the finest. If you do not attain this goal, then Heaven the Equalizer will destroy you.— Zhuangzi: XXIII (Watson Translation)
As we said before, this passage is quoted in the epigraph of the third chapter of the novel. All of the novel's chapters have epigraphs, and nearly all of them (like this one) have a Taoist influence. The majority of them are either by Zhuangzi or Laozi, and it's clear that this is where Ursula LeGuin draws her understanding of Taoism.
It would take forever to analyze every single one of the epigraphs, so let's focus on the one that also gives us our title. After reading the novel, it's pretty obvious which parts of this passage are evident in the story.
The second sentence refers to the sons of heaven being constant. Doesn't that sound like our favorite protagonist? Heather tells us over and over again that George's personality is incredibly constant. He doesn't change. Even when he's sleep deprived and hopped up on caffeine, he's still the same person.
Then there are the series of sentences that tell about how the sons of heaven don't learn, work, or reason things out. Well, we're explicitly told that George isn't a reasoner, and he's often depicted as kind of stupid because he doesn't have a lot of "book learning" or any desire to work hard. According to this translation, this sort of personality is a high achievement, and that is the way Heather and the aliens think about George's personality when they get to know him.
Then there is the final line, and our title. Those who can't do the things the sons of heaven (like George) do will be destroyed in the lathe of Heaven. Well, that's pretty much exactly what happens to Dr. Haber, who is all about reason, work, and learning but fails massively, anyway.