I think this is because it's advice for a corporate environment. Candor works with customers because customers want to know they can depend on you. However as s

I think this is because it's advice for a corporate environment. Candor works with customers because customers want to know they can depend on you. However as someone else in this thread commented, corporate environments have a lot of politics. Other people don't depend on you (or don't perceive it as such) and, to make a blatant generalization, are more worried about keeping their own job. So: work with customers? Be candid. Work in corporate? Don't be candid.