British & Australian, American

to not change or try to improve something that is not causing any problems.

So long as the machine still does what you want it to, my advice is to leave well alone.

Surgeons are aware that every operation carries some risk, and sometimes decide to leave well enough alone.

• nip and a tuck
• nip and tuck
• nip in the air
• nip in the bud
• nip something in the bud
• nitty-gritty
• no call for
• no call for something
• no dice
• nod off
• no doubt
• no doubt about it
• nod's as good as a wink.
• no end
• no end in sight
• no end in sight to
• no end in sight to something
• no end of
• no end of something
• no expense is spared
• no expense spared
• No fear!
• no good
• no great shakes
• no hard and fast rules