If I have the Lucky feat1, it allows me to choose to take a re-roll, to see if I might do better on a d20 check:
Whenever you make an attack
roll, an ability check, or a saving throw, you can spend
one luck point to roll an additional d20. You can choose
to spend one of your luck points after you roll the die,
but before the outcome is determined. You choose which
of the d20s is used for the attack roll, ability check, or
So in the chance of a disadvantaged roll, I can choose to attempt a better roll; but if the outcome is still worse, it does not expend a "luck point", should I choose. Is this the case?
1 Not to be confused with the Halfling's racial trait also called Lucky that works somewhat differently.
According to this question from the Sage Advice Compendium, if you roll with disadvantage and use a luck point, you get to choose which of the three dice you use, effectively turning disadvantage into super-advantage:
It does still preclude using things dependent on not having disadvantage, like Sneak Attack, which Jeremy Crawford reminds us of in this tweet. You can even choose to roll the third die after you've seen the result of the roll.