if it ain't broke, don't fix it

• if it ain't broken, don't fix it

• if it ain't busted, don't fix it.

Attested since at least the 1970s, originally Southern United States English; popularized by T. Bert Lance in May 1977.[1]

if it ain't broke, don't fix it

1. Leave something alone; avoid attempting to correct, fix, or improve what is already sufficient (often with an implication that the attempted improvement is risky and might backfire).

   I know it’s an ugly-looking antenna, but it gets the job done, and if it ain't broke, don't fix it.

• leave well enough alone
• never change a running system

• don’t change a winning team
• don’t change horses in midstream