Wikipedia states:

The so called “law of unintended consequences” (or “law of unforeseen consequences”) is not a true Scientific law such as Ohm’s Law, but a humorous expression in common use according to which any purposeful action will produce some unintended, unanticipated, and usually unwanted consequences.[3] Stated in other words, each cause has more than one effect, and these effects will invariably include at least one unforeseen side-effect. The unintended side-effect can be more significant than the intended effect.

The subject of this sounds suspiciously system-like as it has ‘purposeful action’ ( a human-centric view of the attributes of a system, admittedly) and the results could well be regarded as emergent properties. A bit further into the Wikipedia article suggests that causes might be the complexity. The sociologist Robert K Merton is credited with making the concept popular and he applied it to social systems and suggested that the possible causes of the problem ....