Luck as a Saving Throw
Troika! is the new OD&D. And after looking at these fantastic OD&D backgrounds I was thinking about Troika!'s luck applying to the classic Five Saving Throws.
Experience Beats Luck
When a PC Tests Their Luck if the situation is related to their background their Current Luck does not degrade by 1.
Eg.
A fighter uses his strength to lodge his spear through the handles of a door to keep pursuing monsters at bay. He Tests His Luck to see if it holds but does not lose a luck point.
The same fighter is targeted by a trapped chest. The magical beam shoots out and he must Test His Luck and lose a point of Luck.