Banality of good

The banality of good is a concept of Christian ethics evil deeds carry much more weight than good ones. This truth can be observed in creation in the it is far easier to destroy than to build. A small amount of poison can contaminate a well, but a vast amount of water is required to dilute it to the point of safety, and no amount of dilution can truly remove the poison. This leads to the Christian concept of sin. The Bible teaches that all people sin and are falling short of the 100% standard required of them. Since no-one is able to meet this standard, humans are equally guilty before God of "missing the mark". Whether your glass contains only one drop of poison, or if it contains 50% poison, it's result is the same, the drinkers will end up equally dead.

Ecclesiasties 9:18-10:1 Wisdom is better than weapons of war, but one sinner destroys much good. Dead flies make the perfumer's ointment give off a stench; so a little folly outweighs wisdom and honor.

"The toil of all that be

Helps not the primal fault

It rains into the sea

And still the sea is salt" - A. E. Housman

Analogies

Poison in the cup

Biocides are powerful, but the effect that they have is only negative.  

Game theory

The prisoners dilemma and Nash equilibria.