Prevention is better than cure

Proverbial Meaning: Stopping something bad happening is better than dealing with something bad that already took place.

Literal Origins: It's easier in the long run to prevent a patient from getting sick with inoculations or medicine etc than it is to try and cure them after they are sick.

Common Usage: This proverb is extremely common and used on many different levels, from reasons to build safety rails to stop people falling through to invading countries to thwart ‘evil' dictators. It is used by most people in a genuine fashion, a concern for safety, but sometimes (from a cynical point of view) it can be used as an excuse for more controversial purposes, like the latter example by a politician for instance.