A go to response when things are clearly not fine, but you are going to have to continue regardless, either due to practicality or social responsibility.
Bonus points are awarded if the person you tell things are probably fine to realizes the subtext that "things are clearly not fine" and comes to help you.
Alternatively used to reassure yourself or others when you know what is happening is wrong.
Hey are you OK carrying all those boxes of fragile vases down this steep hill?
Yeah it's probably fine.
On second thoughts maybe I'll take some...
Is it OK to be breaking into your office at 1am?