Externalities

From RationalWiki

An externality is a cost or benefit not borne by or given to the one who should rightly have to deal with it. The clearest example of a negative externality is air pollution. The power plant that emits filthy, sooty smoke is imposing a cost unfairly on its neighbors, instead of bearing it itself. This causes overproduction and overuse of resources that could be more efficiently used elsewhere (such as clean air), since the one making the product does not suffer the costs of dirtying the air. This is one instance where all economists, even the strongest pro-capitalism ones, will agree that government should step in and redistribute the costs in order to keep the economy running at maximum efficiency. This concept is very easy to understand if you're not a Libertarian