Principle of the commons is about downside risk

In the commons we have something to lose.  In paying attention to the principle of the commons, we want to reduce downside risk.

For example, in regard to the commons elements of "quality" and "bad behavior", the "all-it-takes-is-one" principle applies here:  all the high quality, and all the good behavior in the world, can't really offset the negative impact of the single seriously bad offender. 

And it's always a risk-waiting-to-happen.  When/after it happens, it's too late.  Ooops.

We can see in the news the disastrous results of one industry or another which did not do an adequate job of maintaining their commons, and subsequently lost millions/billions as a result of as little as one bad apple; or one avoidable mistake.