Let me give it a shot.
You can make a pretty good guess at what someone might do under a particular circumstance by looking at their past behavior under similar conditions. He might surprise you, but not that often.
Lets say an SF author writes about what Hitler would have done if he'd gotten the atomic bomb in 1943. He might write that he would have put it on the shelf, declaring it too horrible to use in warfare, and become a pacifist. But I think most of us know what the more plausible scenario would have been.
It's not that hard to make educated speculations about how something would have gone when a pattern of behavior is obvious. Of course, nothing is certain, but you can bet on a scorpion acting like one most of the time.