The 'a career that wasn't known for it' emphasizes that that the job requires intelligence. The plain way of saying that is, as you suggest, that she hadn't survived a long time in her job by being stupid. However, if you want to emphasize the qualities needed for the work, and if you want to vary your style, then you can say it this way. Example: Great athletes don't win races that are known for their toughness by being wimps. (a wimp is a weak, feeble, ineffectual sort of person) Example: Microsoft didn't get to the top in a field known for its competitiveness by being diffident in its approach. And an example that is nearer the original in the question: Africa can be a violent place politically. The weak and powerless often sink into obscurity. Robert Mugabe hasn't stayed in power in a country that isn't known for it by being tolerant and gentle. It might be clearer if worded differently: Mugabe hasn't stayed in power in a country that isn't known for its tolerance by being gentle and forbearing (forbearing = tolerant... and avoids repetition). I prefer the style where the IT is defined. However, it works well provided you read the passage as a whole and don't try to translate bit by bit. This is only for advanced students. It will give anybody below advanced a headache.

The "that wasn't known for it" indicates that her career is generally a short-lasting one, instead of one where someone might expect to be employed for a very long time. "And she hadn't had longevity in her career by being stupid." This still conveys 2 of the parts of the author's sentence: that she has been in her career for a while and that she hasn't acted stupid. But it leaves out the information that her career is something that you wouldn't expect to last for a long time. Assuming it's a desirable career, the added meaning from the "that wasn't known for it" is that she is in someway impressive or better suited to that career than the average person in it, perhaps because most people burn out quickly or aren't good enough to last in that career. The writing is acceptable, but based on the other two sentences you posted, not particularly good or sophisticated.

How else could we, as "would-be writers" communicate the same thought. "She wouldn't do that, because she is not stupid." "She is not known for being stupid." "People in her chosen profession are not typically, stupid people." "That profession is not known for the stupidity of its practitioners." If we are wise Dimitriy, I think we do well when we question both the intelligence and expertise of all authors. In all honesty, there are published works which probably should never have obtained to publication. Still, neither you nor I have anything to do with that process. We can ridicule the hell out of dull witted publishers and writers though, until they cease to seek publication of nonsense.

Not sure what the fuss is here. A perfectly adequate sentence accurately explained by Chris.

Hello Dimitriy The meaning is a very simple one. It is referring to a woman, and it reminds readers that she worked in a require that required much education and intelligence. The point being, that the woman was not "stupid". It must be presumed by readers (and the book's characters) that this was a very smart woman. The author could have written as you suggest. Your analysis is reasonable; BUT...that is not what the author wrote. The point me to make here is to show you that author's of books, do not always write well, or clearly, or succinctly. As a book reviewer and critic of literature, I can tell you frankly that many books are written quite badly in fact. If you have a sense of this (and apparently you do) then you are well on your way to being a clear thinker and a quick analyst of clear communication. Well done I say.