Warning: The following paragraphs contain a large number of spoilers, so stop right now if you don't want to be spoiled.
At different points in Charles Stross's Iron Sunrise, Herman explains to Wednesday why he knows what to do before things actually happen:
The Eschaton preserves global causality [...] by recursively transmitting information back in time to itself, which is used to allow it to edit out temporal anomalies. I receive orders from deep time and execute them knowing that in doing so I ensure that the descendant state vector is going to exist long enough to issue those orders.
He also tells her why he was not able to prevent the destruction of her home-world:
If I do not receive such orders, then it may be that the events are not observable by me. Or my future state vector. This situation may occur if the Eschaton is disrupted or edited out of the future of this time-line.
Later, he explains to her what he believes to be the ReMastered's plan
The ReMastered focus on assassinating Muscovite diplomats is itself suggestive, although I am not yet certain of their motives. The faction responsible appears to want to force the Muscovite diplomatic corps to send the irrevocable go code to the R-bombers, thus precipitating a political crisis on New Dresden with implications elsewhere. But it is difficult to be sure.
But he was also able to pick Wednesday at a young age and train her so she was ready for certain future events. Near the end, he even advises her to "Keep your jacket by you at all times." because "You never know when you'll need it.". This advice seems quite well informed since it ultimately saved her life.
How could he know this if the events are not observable by him? How could he ignore the real motive of the ReMastered? Is he telling the truth about his knowledge of the situation?