Error by dualist design

It seems that if we postulate the existence of spirit as non-physical, and that they cannot directly act on physical laws, then it's likely sufficient to deduce the existence of fundamental errors (or at least randomness).

Let's say we created a simulated reality, where we design a 100% closed system that can be explained by the laws within itself without reference to the the outside (our human) world.

But as part of the design, we want human operators to have influence over it. More interestingly, we want humans to be able to control (at least to some extent) the entities in the simulated world.

Then, we'd have to introduce "errors" or "randomness" or "fundamental limits to cognitive ability" so that this is possible.

If everything was perfectly known, then it would be impossible for the world to have dualistic properties.