“If it ain’t broke, don’t fix it.”

What does it mean?

Don’t try to improve something that already works fairly well. You’ll probably end up causing new problems.

Where does it come from?

It’s been a colloquial phrase in the southern states of the USA. For example, this piece is from the Texas newspaper The Big Spring Herald, December, 1976:

“We would agree with the old Georgia farmer who said his basic principle was ‘If it ain’t broke, don’t fix it.'”

The phrase has to be American. In England things don’t get broke, they get broken. ‘Ain’t broke’ is intended as a knowing southern yokelism, as opposed to ‘proper’ American, but it is one that wouldn’t have originated anywhere else.