Determinism in martial arts

One kind of nutty idea in some martial artists' minds is determinism. That is, the idea that, "Bad guy does A and I respond B which causes him to do C, to which I respond with D, forcing him to fall like so..." This idea of cause and effect is tenuous at best. Actions don't cause other actions, though they do influence them. James Ebert quotes Vietnam war army lieutenant James McDonough:

We would learn how little our decisions determined our futures. Rational decision making or technical and physical skills may save you once or twice. But a man in combat is exposed a thousand times. A gust of wind blows at the right moment to take a mortar round ten yards farther to explode. A tree grows fifty years only to absorb a grenade fragment that would have otherwise entered your heart. A blade of grass or bent branch deflects a speeding bullet enough to send it harmlessly through your flopping shirt - or savagely through your brain or liver. (from A Life in a Year)

I don't intend this to suggest fatalism. It is wiser to stand behind the 50 year old tree than beside it when people are shooting at you. You can improve your chances intelligently, but you can't determine your own future absolutely. You must build your martial system around probabilities and tendencies, not pre-determined cause-and-effect events. So, how do we figure out the probabilities of a given thing happening or the likelihood of a technique working a certain way?

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Randori - and lots of it. A system without randori (or sparring or push-hands or freeplay of some sort) is simply not a martial art. randori - and lots of it. That's why Kano's Kodokan judo excelled over the koryu jujitsu players they went up against. That's why the Gracies excelled in the 1970's and 80's in Brazil.
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Randori - and lots of it.