What makes you think that decision making in our brains is free of "regular certainty in physics"? Deterministic systems such as weather patterns can be unpredictable enough.

To be fair, if there's some butterfly-effect nonsense going on where the exact position of a single neuron ends up determining your decision, that's not too different from randomness in the mechanics of physics. But I hope that when I make important decisions, the outcome is stable enough that it wouldn't be influenced by either of those.