Also,
let well enough alone. Do not try to change something lest you make it worse. For example,
This recipe has turned out fine in the past, so leave well enough alone. The idea behind this expression dates from ancient Greek times, specifically Aesop's fable about a fox who refused a hedgehog's offer to take out its ticks lest, by removing those that are full, other hungry ones will replace them. Put as
let well alone from the early 1700s, it was first recorded as
let well enough alone in 1827. Also see
let sleeping dogs lie.