Comment by meheleventyone

The example is really bad for this because it doesn't say the result is non-deterministic, just complex and treated as a black box which only makes the result hard to reason about when abstracted rather than truly non-deterministic.

A common example from my domain is making floating point math deterministic. This is fairly straightforward for a single operating system/piece of hardware combination but as soon as you need cross-platform determinism is full of gotchas. In particular because the abstraction in this case is often the programming language, the specific compiler used (sometimes even version) and standard library. This also gets as subtle as not being able to use certain instructions like fused multiply-add and SIMD intrinsics where the implementation can differ between pieces of hardware.