I just read through the book excerpt about your boss not being your friend so don't divulge too much of your personal life as it could get in the way of your work life.
In general, I agree with the sentiment and in the context of the example you gave, it makes sense. But there's also a management philosophy that says, basically, to treat people like humans; that means take into account their whole being, not just their work being. Empathize with them. Maybe they haven't been performing to the level you're used to seeing them perform, for example. That may be because of personal reasons. As a boss, you might want to be curious about that and see what you can do to help. That does involve talking about things outside of work because it has a direct effect on things at work.
So where is the line drawn here? If, say for example, you're going through a difficult period personally and your boss doesn't know about it. Would it be fair to you and your boss to keep them in the dark? How much should you divulge? I think I know what my answer to this would be but what would you do, Ken?
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