I think what Ilya is trying to get at here is more like: someone very smart can seem "unpredictable" to someone who is not smart, because the latter can't easily reason at the same speed or quality as the former. It's not that reason itself is unpredictable, it's that if you can reason quickly enough you might reach conclusions nobody saw coming in advance, even if they make sense.
one could be about maximising wealth while respecting other human beings, the other could be about maximising wealth without respecting other human beings.
Both could be presented same facts and 100% logical but arrive at different conclusions.
I think it's important for us to all understand that if we build a machine to do valuable reasoning, we cannot know a priori what it will tell us or what it will do.
"Prediction" associated in this particular talk is about "intuition": what human can do in 0.1 second. And a most powerful reasoning model by its definition will arrive at "unintuitive" answer because if it is intuitive, it will arrive at the same answer much sooner without long chain of "reasoning". (I also want to make distinction "reasoning" here is not the same as "proof" in mathematical sense. In mathematics, an intuitive conclusion can require extrodinary proof.)
Just look at inductive reasoning. Each step builds from a previous step using established facts and basic heuristics to reach a conclusion.
Such a mechanistic process allows for a great deal of "predictability" at each step or estimating likelihood that a solution is overall correct.
In fact I'd go further and posit that perfect reasoning is 100% deterministic and systematic, and instead it's creativity that is unpredictable.